10 Myths About Fuel Economy

10 Myths About Fuel Economy

It’s ironic that though we live in a time when information was never more plentiful that misinformation, fallacies and myths persist.

No doubt that lead-out sentence could launch a discussion on myriad subjects, but looking at a relatively benign one – vehicle fuel economy – people still entertain notions that are simply not true.

And whether misconceptions are really benign is also in question because despite allegations to the contrary, ignorance is not always bliss.

In the case of cars, the automobile has been called the second-most expensive purchase many will make, and marketers also have something to gain or lose depending on what you may think about saving money on fuel.

ALSO SEE: Why is My Gas Mileage so Bad?

For instance: is it best to pick a dinky little econobox to save the most gas? Should you use premium fuel when regular is called for? Should you dump in fuel additives to increase economy, or is that just snake oil? How long should you let a car warm up, or should you do it at all? Should you replace an aging car on the assumption it can’t get as good of mpg as it did when new?

Following is a list derived from U.S. EPA data that answers these questions and others. A couple of the list points merely clarify the EPA’s role, a couple are just general good info to know, and several hope to help you make better financial decisions – be they from small retailers up to the kind of vehicle you choose and how soon you should choose it.

1. Myth: Letting a vehicle warm up is best for gas mileage


This holdover from the good old days persists, but modern cars are designed to drive within a few seconds of being started.

Letting them sit and warm up may be convenient – like in the winter to defrost and warm the interior – but this does not save gas. A car gets 0 mpg as long as it is sitting.

It is true an engine must reach an optimal operating temperature for best fuel economy, but manufacturers often recommend gently taking off, and letting the engine warm up as it’s carrying you down the road. It will warm faster if you do this while avoiding heavy loads until the engine temperature comes up.

2. Myth: A vehicle’s fuel economy decreases with age

If your car is 4 or 7 or even 10 years old, is it starting to become less efficient? Should you therefore think about replacing it?

Well, you may want to just to get a more-efficient newer car, but as for whether it has dropped from original spec, assuming it’s maintained, it should be OK.

“Vehicles that are 10 or even 15 years old will experience little decrease in fuel economy if properly maintained,” says the EPA.

3. Myth: The smaller the car, the better the fuel economy


This also used to be true before the advent of newer technologies, and the idea hangs on. The most efficient little non-hybrid car sold is the 40 mpg Mitsubishi Mirage. A Toyota Prius c hybrid actually is a chart topper at 50 mpg, but many bigger and more powerful cars are also competitively efficient.

ALSO SEE: Top 10 Most Fuel Efficient Hatchbacks Under $25K

Fuel saving technologies besides hybridization, including direct injection, turbocharging, low rolling resistant tires, and even – despite the VW scandal – diesel engines. About half of the 2016 model year cars on the EPA’s top 10 list are midsized or large cars or wagons, as a matter of fact. Most are hybrids.

Not far behind the Prius c and well ahead of the Mitsu is the 2016 Chevy Malibu Hybrid projected to get 47 mpg. It is a large-ish midsized sedan – much more roomy, comfortable and safe than a subcompact conventional econobox.

4. Myth: The federal government tests fuel economy for all vehicles

Actually most passenger cars and light-duty trucks are subject to testing, but federal law rules out testing for vehicles over 8,500 pounds.

This means no official fuel economy rating is required for trucks that can do duty for passengers like the Ford F250/350, Chevrolet/GMC 2500/3500, and Dodge 2500/3500 vehicles. These exceed this weight limit and are not tested.

5. Myth: EPA window stickers are a form of guaranty on fuel economy

After hearing “your mileage may vary” enough times, hopefully most people do not think the fuel economy certification is a federal vouching for the stated number.

In case you did not make this connection, the EPA writes its own qualification on the subject.

“The primary purpose of EPA fuel economy estimates is to provide consumers with a uniform, unbiased way of comparing the relative efficiency of vehicles,” says the federal government. “Even though the EPA’s test procedures are designed to reflect real-world driving conditions, no single test can accurately model all driving styles and environments.”

There are too many variables to account for including how people drive and even the type of gas put in the car. Ethanol at a 10 percent mix with regular gas can decrease fuel economy by around 3 percent, says the EPA.

6. Myth: Manual transmissions get better fuel economy than automatics


Do you hear that? That’s the imaginary loud buzzer for Wrong Answer! It is no longer a given that manuals trump automatics for fuel economy.

Advanced automatics may now net the same or better fuel economy than a vehicle of the same type equipped with a manual – though there are exceptions here as well.

The type of transmission used in most hybrids and now being used to optimize conventional cars – CVTs (continuously variable transmissions) – also tend to do better.

ALSO SEE: 10 Cars That Only Come with a Manual Transmission

Drivers however have pushed back, and some enthusiasts have said they can’t stand CVTs or simply prefer the feel and control of a manual. Even the new dual-clutch automatics that may be manually shifted have experienced vocal detractors now that these have been on the market several years.

And, a well-operated manual may still yield great results but the watchword is how well it is operated. Meanwhile automakers have largely moved away from offering manual stick shifters in types of cars that used to have the option.

7. Myth: It takes more fuel to start a car than allowing it to idle


The advent of stop-start technology ought to be proof enough this is a myth. In case you did not get the memo however, idling may use a quart to a half-gallon of fuel per hour at a cost of 1-2 cents per minute.

One should thus turn off the engine when sitting still, except when in traffic or waiting in line. New engines start very well and efficiently, especially when warmed.

8. Myth: Premium gas yields better economy than regular

Do I Really Need Premium Gas?

“You will probably experience no benefit from using premium fuel over regular,” says the EPA to anyone whose engine is not specified to be premium-only, or in the case of engines that don’t otherwise knock on regular.

Otherwise, if it runs on regular, use regular. The extra octane of premium and plus do not improve economy says the EPA, but they will cost more to fill up.

ALSO SEE: Do I Really Need Premium Gas?

9. Myth: Replacing the air filter helps fuel economy

This one sounds like common sense, but the fact is modern fuel injected engines compensate for dirty air filters by reducing fuel to the air-fuel mix.

Again, this is a holdover truism from the days of carbureted engines, and those are adversely affected by dirty air filters.

Otherwise, changing a dirty air filter – while still generally recommended – is not a means to save fuel. It may improve power for a freer breathing engine, as the fuel mix may be increased also.

10. Myth: Fuel additives or bolt-on devices can increase fuel economy

Add-on aftermarket devices you may buy and install, despite claims by their marketers, are not vouched for by Uncle Sam – specifically the Federal Trade Commission.

Same goes for stuff you find at the auto parts store, or what not that promises better mpg if you dump it in with your fuel.

If you or someone you know has personally tried something and feels differently, subjective impressions may allow for that, and this is a controversial subject and a huge aftermarket business.

For its part, the feds urge away from believing these claims.

The only modifications the EPA will sign off on are comprehensive full conversions that meet all EPA certification standards.

This story originally appeared on HybridCars.com

  • Jonny_Vancouver

    Cool, thanks for clearing that up! I have to admit to idling on winter days because my cars get grumpy if I don’t. No joke, they seem to drive smoother for the day if I give them 5 or so mins to warm up on cold days, and they drive rougher if I don’t …

  • smartacus

    my preferred method for increasing gas mileage is avoid using brakes.
    Taking the turns on 3 wheelz negates the need to accelerate up again.

  • Diesel Driver

    They didn’t mention the simplest method of improving fuel economy. SLOW DOWN. My dodge Diesel pickup with the Cummins engine and a 6 speed manual gets 17 mpg at 70, 19.5 at 65 and 22.5 at 55. That’s with no trailer and on the interstate 40 between Mojave, CA and Kingman, AZ includes both directions filled up at one end (Arizona of course, the fuel is a LOT cheaper there). I even did one tank on normal around town and between California City and Lancaster accelerating normally but only doing 45 mph and got 25.9 mpg. It was really difficult to keep the speed down though. Keep your foot out of the loud peddle and use your cruise control whenever you can. Like smartacus below says, using the brakes does require you to use more fuel getting back up to speed on the other side of the turn but be safe. I’m sure he’s just kidding.

  • Jeff T

    What does Vancouver know about winter? From northern Ontario.

  • Jeff T

    Your right when you say that. Just have to manage speed and the extra cost of the time you spend driving on the highway. Racing to the red light though is something I see 20 plus times I see everyday.

  • Clearly you need to take the next step and just start drifting. 😉

  • I live in Florida. I may spend a little extra idling in some situations, but when a car interior can heat up to 135 degrees F during the summer (meat is considered cooked at 165, to illustrate some scale), it can be necessary to keep the people inside the car alive and healthy.

    Well, as healthy as we Floridians ever get.

    Also, no mention is made of MPG per occupant. Single-occupant vehicles are much less efficient than carpools.

  • RyDaddy

    On this same note is why, with proper technique, an automatic will NEVER compare to a manual transmission for maximizing MPG; the ability to COAST. Pop a manual tranny into neutral and you have mechanically disconnected the engine from the speed of the vehicle, something that can’t be done on an automatic where you are always coupled through the torque converter. Allowing the engine to idle and burn minimal fuel while you are cruising at full speed downhill or across flat ground or slowing gently to the next stop sign.

  • Godless Heathen

    You can also pop an automatic in neutral but doing so with either transmission in most newer cars will actually use slightly more fuel. Engines use fuel to idle but most newer cars use no fuel during deceleration so “coasting” in neutral to save fuel should be myth #11.

  • RyDaddy

    Sure it is; maybe it only applies to a diesel, which needs next-to-nothing to maintain an idle, but both my brother and I are coast-masters and we both get 50+mpg in our diesel Jettas. When my wife borrows my car, she never takes advantage of its massive coasting ability and she gets 47mpg, tops.

  • Godless Heathen

    In newer gasoline cars there is no fuel flowing to the engine during deceleration. If you put the car in neutral fuel will begin to flow to the engine. You can look it up, not only is coasting dangerous in all vehicles, it wastes fuel in newer cars.

  • Stephen Nichols

    Even the automatic Diesel Jetta’s now are programmed to take advantage of engine braking where no fuel is being burned on deceleration. It also saves wear on brakes. Coasting is an old myth from carburetor days. With a carburetor, as long as the engine is rotating it will suck fuel in, even though it may not be needed to stay running. On the other hand, Fuel injection and auto’s(and manuals) can be programmed to shut fuel off completely when decelerating.

  • smartacus

    aw yeah! i gotta do my part to increase fuel economy by drifting.
    It’s for the children 🙂

  • RyDaddy

    But in both cases you are still slowing the car down with the engine, so you are covering less distance than you would if the car was not slowing down as quickly, thereby needing to burn fuel under load and increased RPM to get the car to the same place you could have gotten to with the engine under NO load and at idle by coasting.

    Think of a car as a machine that turns liquid fuel into momentum;

    1) You can choose to convert this momentum to heat quickly using the brakes.

    2) You can choose to convert the momentum to heat slowly by using engine braking (coasting with an automatic since you can never dis-engage the torque converter).

    3) Or you can choose to convert this momentum to heat very, very slowly by only using the friction in the wheel bearings; coasting with a manual tranny in neutral.

    You only need to burn fuel to regain or maintain momentum, so the less momentum you lose (or the longer period of time and thus, distance, over which you loose it), then the less fuel you need to burn.

    Its just force conservation. And if you happen to be going downhill, you are converting gravitational potential energy into momentum without burning hardly any fuel. That’s recovering energy you spent money (on fuel) to gain when you drove uphill initially.

  • C-130Guru

    My 2007 2500 5.9 with 4 speed 48RE gets 21.5-22 MPG @76 MPH / 2150 RPM. Get 15 MPG towing my fiver, keep her in the sweet spot 1900 RPM around 65 MPH. The Edge Juice helps too. But I like it more for the gauges, turbo and EGT protection. Well worth the money for those alone.

  • Diesel Driver

    Your 2500 probably weighs a lot less than my 3500, probably has 3.54 gears instead of my 3.73’s. I had a 99 4X4 2500 and I got 22 mpg at 70 as well. But I felt better having the added stability of my dually for my 30′ weekend warrior that I got for nothing. The WW’s had a reputation for being much heavier than advertised. Plus I hated towing with the auto 4 speed and super loose converter. Torque peak at 1600 per the books and magazines yet when I would get on the throttle hard it would jump up to 2500 rpm. Didn’t make sense to me. If I could have that truck back with my 6 speed I’d be a happy camper (I’d sell the stupid trailer and stay in motels.).

  • Diesel Driver

    You and me both. You can see from my picture though that I’m an old fart and so I am expected to be slow… LOL

  • Diesel Driver

    Like some of the other respondents say, the new EFI’s shut off the fuel to the engine and in some cases shut the engines off when stopped at a light, they also unlock the torque converter so you get less or no engine braking. They have specific settings in newer trucks to set it to a tow setting so it turns that feature off. When I was learning to drive back in the 60’s part of the test in CA was a question about putting your car in neutral when coasting or going down hill and their desired answer was to never do so because you were less safe. Right. My truck driving instructor nearly had a fit about one of the other guys doing that. On the other hand it was a wonder he didn’t pop a blood vessel every day. He was one of the most even tempered men I’ve ever met…Always mad.

  • Diesel Driver

    There are very good reasons for that. Cold fuel and cold engine parts do not favor the vaporization of your fuel and it isn’t going to burn if it doesn’t vaporize. They do the best they can with various crutches to make up for it but nothing can make up the difference except having enough heat in the engine to vaporize ALL of the fuel injected. That requires energy to be expended. I has always bothered me that modern car heaters take heat away from the engine coolant just when the engine needs it as much as the passengers. My parents had an old Kaiser that had underseat heaters that actually burned some gas and blew hot air almost the instant you turned them on. Would be mighty fine to have something like that on a cold winter day. I’ve idled my dodge and even in hot weather (needed the a/c, it being over 100 out) it would still drop the water temp down to the lower part of the gauge instead of slightly over 180 when it was moving.

  • Godless Heathen

    Copy and paste from Wikipedia:
    “When coasting with the engine running and manual transmission in neutral, or clutch depressed, there will still be some fuel consumption due to the engine needing to maintain idle engine speed. While coasting with the engine running and the transmission in gear, most cars’ engine control unit with fuel injection will cut off fuel supply, and the engine will continue running, being driven by the wheels. Compared to coasting in neutral, this has an increased drag, but has the added safety benefit of being able to react in any sudden change in a potential dangerous traffic situation, and being in the right gear when acceleration is required.

    Coasting with a vehicle not in gear is prohibited by law in most US states. An example is Maine Revised Statues Title 29-A, Chapter 19, §2064 “An operator, when traveling on a downgrade, may not coast with the gears of the vehicle in neutral.”

    If you’re coasting to stop signs and traffic lights during normal driving, you’re using more fuel, idling engine vs zero fuel consumption.

    If you’re coasting down steep grades the only way to burn less fuel by coasting is to turn off the engine, good luck with that and don’t let the police see you do it. Most late model automatics will unlock the torque convertor making it easier to maintain speed with no throttle down grades which will render the same fuel economy as turning off the engine, but it is legal and safe.

    If you prefer to put yourself and others in harms way to save a few ounces of fuel then you need to get a second job or talk to a psychiatrist about your harebrained notions.

  • nefnm .

    Myth # 11 You can trust the EPA and the Feds.

  • Godless Heathen

    I remember when neutral was referred to as “angel gear” when used to coast down a mountain in a semi. Since I live in Georgia I call it “Georgia overdrive”, something I heard in a Red Sovine song I believe.

    My wife’s Mazda 6 grand touring with the “Skyativ” technology is one of the cars that is more fuel efficient with the auto trans compared to the manual. I checked the mileage on a trip from Georgia to Delaware and go 40.2 mpg and 40.6 on the return trip. That is with cruise control set at the speed limit, windows up and A/C on. The Mazda 2.5 engine has 13 to 1 compression ratio but runs on regular gasoline!

    DFCO (deceleration fuel cutout) has been around for a while. I was reading about advances GM and others have made on torque convertor clutches, etc. On some models the engine rpms drop to ~ 1,000 after throttle lift off providing minimal engine braking but still allowing DFCO. The result is a long coast using zero fuel. It has to do with whether the torque convertor is driving the drive train or being driven by the drive train.

    I’m a stickler for the rules. My work requires intense safety training and that has carried over to my driving habits. I obey all traffic laws, do the speed limit, never tailgate and come to a full stop at stop signs etc. By doing so I have a spotless driving record, low insurance rates, I don’t get the stone chips and broken windshields that many tailgaters deal with and my autos maintain maximum resale value. Coasting in neutral is just nuts.

  • Snake

    What unnerves me is going downhill with a 2002 F350 and a 30 ft 5th wheel and NO exhaust brake. I know, get one. Sorry , retired senior citizen, no more $$.

  • Ray J.

    Had a new HP fuel pump put in my 2000 Dodge 2500 diesel. Mileage went south from 18-20 free running on freeway to 13???? “WHAT”. Anyone know about a “restrictor”? fact or myth.

  • CrazeeCarl

    I always add a gallon of distilled water with each fill up..Yeah, sometime there’s a bit of sputtering, burping and coughing…But whattya gonna do?

  • Andrew

    Economy aside, things like premium fuel and fuel injection cleaners definitely help with performance and longevity. And of course nothing beats a good old oil change every 5k to 7k to guarantee a long lasting vehicle.

  • swsl

    They say that the most efficient way to heat up an engine is to put it under load promptly, though not heavy load until warm. Idling to warm up is much slower and will keep the engine running cold and inefficient for a longer time.

  • gwayne

    Coasting out of gear may be against the law, but it works as my computer tells me on my 2000 Dodge 3500.Like you said cruise control works and at 50 I’m getting over 25 MPH. When I had the really bad gear venders overdrive that I would never have installed if I knew it came from England I got over 35 MPH , but it was with reverse clutches that wore out often and was not economical with the often and expensive fluid change needed and the cost of a replacement rebuilt unit that more than made up for the savings.Gear Venders O/D units are pure trash and nothing less.

  • Konrad Checinski

    Wrong on premium fuel. Its not premium, its a different octane, if your car is not designed for high compression, why would you run premium? Zero benefit, and money down the toilet.

  • Raymond Chuang

    One myth for many years suggested that opening the window instead of running the air conditioner would reduce fuel consumption.

    Well, I believe it was Volkswagen’s Audi division that proved them wrong–they found out that when you travel faster than 70 km/h (43 mph), the fuel economy loss from open windows was higher than closed windows with the air conditioner running. This is especially true with modern cars with aerodynamic body shapes, where open windows have huge effect on fuel economy.

  • Raymond Chuang

    It really depends on the type of vehicle. Given the aerodynamics of modern automobiles, up to around 120 km/h (74 mph), there’s really not much difference in fuel economy between 100 km/h (62 mph) and 120 km/h.

    On a pickup with its less efficient aerodynamics (even on modern models), the fuel economy starts to drop pretty dramatically at higher speeds, similar to what older cars do.

  • Charles Vamos Jr

    Some premium fuels have detergents that lesser octane fuels do not.

  • Deuce_2112

    Where I live, Regular Gas has 10% Ethanol, and it’s utter shit. The only way around it, seeing as my car was designed to run on gasoline and not horse piss, is to run 94 octane supreme. And yes, you can tell the difference.

  • Wayne Wilkie

    Mythbusters did the research and field testing.

  • Wayne Wilkie

    Oil company Bullshite!

  • Wayne Wilkie

    Coating in neutral with a rig going downhill? “Mexican Overdrive”.

  • otterdriver

    I track fuel consumption religiously. Yearly cost per mile for my ’11 Tacoma between regular (18.2 mpg on stock tires and suspension) and premium (19.8 mpg lifted on 32″ tires) are nearly the same when driving empty, the extra distance I travel without having to stop at a fuel station is a bonus. I tow regularly and the benefits of the higher octane premium go without saying when the engine is loaded and timing retards to avoid knock. Add to that some brands of premium have no ethanol and it’s a no-brainer for running in engines that operate seasonally (boat, mower, snowblower, saw and generator in my case).

  • Tony4645

    I wouldn’t believe something like this just because they did a test on one particular vehicle. There are too many variables that can change all that. How much were their windows? Was it opened two inches or were they wide open. How many windows were open? Did they have a rear-rear window or a rear-side window too? If you open all your windows, including the rear-rear window, there would be less resistance. How about opening a roof-top window, which operate quite different from one brand to another car/truck brand. Most people won’t ride their vehicle, at those high speeds, with their windows open because it is too deafening. So actually your AC will reduce your mileage. I know only a few people who will drive with their windows open instead because they believe the fresh air is better for them and they believe the AC air causes fatigue.

  • Tony4645

    It has already been tested and proven on these new vehicles that they make no difference with the mileage because the computer already compensates for the regular fuel by changing the air/gas mixture. They had the vehicle hooked to a computer to show three different tests and the higher octane actually made the vehicle run worse. The only time you need premium, or when premium will give you a better mileage, is when you are driving an old vehicle with a carburetor, or any yard tools like your snowblower, lawnmower, weed eater or any two cycle engine because the ethanol will cause havoc as when it sits in the tool for a long period of time. It will cause it to build up with gunk that looks like hard caramel. I have seen it on the fuel line and carburetor when a mechanic showed it to me when he sold me a brand new chainsaw. The build up was like 1/2 inch thick and the fuel line was very brittle.

  • What needs to be said about letting your car idle in -0 freezing weather is that probably one of the biggest reason for it is the petroleum based oils’ viscosity. In other words it becomes less fluid compared to quality synthetic which stays fluid at extreme cold temperatures.

  • Zachary Smith

    Playing fast and loose with some terms. Fuel economy and efficiency are not the same thing at all.

  • callmebob

    Curious what year of vehicle ?

  • callmebob

    synthetic motor oils (of the type used in small vehicles) are also crude based.
    it’s just filtered/refined substantially more to render it more uniform at a molecular level and remove impurities.

  • Mike Smith

    That depends on the type of synthetic oil you’re using. It isn’t all from the same base stock.

  • callmebob

    What brands/types aren’t ? I had just had the discussion with a guy in marketing at Mobil a couple of months ago and he confirmed what I’d read elsewhere. He claimed that only really high end racing and industrial products labeled as synthetic were NOT crude based.

  • BDJ

    “it’s just filtered/refined substantially more”

    Um, no it’s not. There’s refining, and there’s chemical processing…they’re not the same thing.

    Synthetics (hint: it’s right there in the name) use a chemical process to create and manufacture. Blended uses distillation/refining.

    The key is in the name. It’s synthetic. As good as )or better), but not the real thing. Conventionals just so happen to work well with engines and moving parts, so they discovered. YAY! However, synthetics are DESIGNED to work with same.

    When you think about it, something that was discovered to work well with, or something that was DESIGNED specifically for use with…which would you prefer?

    This is also why synthetics are priced more. They are designed to work better. They also have significantly less downside than conventionals.

  • callmebob

    Synthetic motor oils are almost exclusively derived from crude stocks – I had added a part in box brackets after initial post when it was clear that my filter/refine didn’t include other chemical processes – to me that’s just part of the full processing of it (not your basic distillation process). Does that text with chemical processing show up or does the commenting system somehow hide it because it’s in box brackets ?

    “synthetic motor oils (of the type used in small vehicles) are also crude based. It’s just filtered/refined substantially more to render it more uniform at a molecular level and remove impurities. [ I’m going to add something later – that filtered/refined ought to include chemically processed as well, as I’d forgotten that is wasn’t all distillation column driven ] “

  • It’s called “drag” when you drive with the windows open and YES it does reduce fuel economy. I don’t care what you drive or how open your windows are, there is still a huge amount of drag. Hence the aerodynamic body designs. It’s common sense.

  • Yup, you are correct and I’ve seen accurate tests. No gain on the average car with premium at all. No average car gets an ounce more fuel economy or performance running premium. It’s an utter scam. High performance cars are the only that gain from premium and all they gain is a bit more power, nothing else.

  • You are right about the ethanol and seasonal. That stuff is shit in seasonal equipment and gums up seasonal equipment. Farmers refuse to use any gas with ethanol and gas stations in those farm areas will not carry it sometimes and advertise no ethanol, even in their regular grade. It does not store well at all and gels up faster than no ethanol. You do get more power from premium for towing, yes, absolutely, but on the average vehicle not towing, there is zero gain for premium. Tests have proven it.

  • Ethanol is utter shit. Especially in seasonal equipment. It gels up too easily a clogs seasonal stuff.

  • Even lesser fuels have detergents now too.

  • Ahhh, the old “feather the pedal” technique. There is much to be said for that! It actually does reduce fuel consumption over gunning it from standstill and there is plenty of proof for it. Anyone can see the difference. Remember the old myth that 4 barrel V-8’s used so much more fuel than 2 barrel? Nonsense. Not if you knew how to drive them proper. Just take off slow. Cruise control does not save gas though on hills, it actually wastes gas. On flat roads it helps cause it keeps you off the pedal, but on hills it is unnecessarily braking going down and going up hills it is wasting fuel keeping constant speed while climbing. It sucks on hilly areas and I turn it off cause I can do way better.

  • Exactly. Lol. I’m from Northern Ontario.

  • NaOnly

    I’m interested in what difference you can find. Regular and premium have virtually identical BTU content, and that ethanol only accounts for and energy loss of some 3% possible energy, and when you mix in the efficiency (or rather the lack therof) of putting those BTUs to the ground, it’s a difference one could call negligible. On top of that a vehicle that is safely tuned to 87 octane absolutely will not experience benefits from higher octane fuels unless there is an additional issue causing fuel detonation. It simply won’t happen. Octane is a fuel’s resistance ignition, nothing more, nothing less. Unless you’ve found a way to up your compression ratio, timing advance, camshaft timing, or the design of your heads your butt dyno is lying to you.

  • NaOnly

    That’s really all dependent on gearing though. I make better fuel economy at 70 than at 55. I have a 2.82 rear so for me the RPM difference between 50 and 70 is small enough that the extra ground I cover in the time it takes to consume a gallon of fuel I’ve traveled more miles at 70 on a gallon than 50. I get about 22 at 50 and close to 26 at 70. Car is a 2007 charger for reference.

  • otterdriver

    I feel I need to clarify myself over premium. It’s advantage lies not in a more energy-dense fuel but in it’s ability to delay the onset of knock. Nothing to do with an ECU changing fuel/air mixtures. I’ll generalize things here as this probably isn’t the place to dissect compression ratios, flame front speed, temperature, optimal fuel mixture, etc. Generally speaking, as an engine begins to retard timing to delay knock (not the normal timing delay that occurs over the RPM/engine load band) your efficiency goes out the tailpipe. If you can maintain optimal ignition timing by not having the knock sensors interfere, higher cylinder pressures are retained, their occurrence is optimized in the power stroke and more efficiency is realized. As previously stated my mileage is almost 10% better on premium fuels. This isn’t an anecdotal number, it’s calculated and averaged over the life of the truck. The nature of my driving is mostly highway and the engine is always under load. If you drive an aerodynamic car and the engine loafs on the highway, or spend lots of time idling in traffic then you probably won’t see a measurable difference as the engine is under a light load and the knock sensors never come into play. I have 140K of fuel consumption records on this truck and premium consistently gets better mileage. I attribute this to its ability to run more advanced timing under load. If my theory isn’t sound then my bad, but my consumption records don’t lie.

  • Tony4645

    Bill Dent I know all about drag and my point still stands. Every vehicle’s shape is different. Every vehicle have different windows. Some have no rear window to open, some have a small rear window that opens, some have full rear windows that open. Their level of drag is going to be very different. I can open my whole rear window on my Toyota that allows a lot more wind to pass through interior, creating less drag then a standard truck/car/van. Why do you think they created the rear window to open up and the side windows, on a minivan, to open sideways instead of up and down? Are you getting the picture yet or do I need to go further with this discussion? The fuel you are saving by having no tailgate, to a box cover is only a few pennies. I can say that because I drive a dodge longhorn with a Diamondback cover for locking up my tools or hauling any toys on it and my truck is pig of fuel regardless.
    When it comes to rooftop windows, they have designed them so much better then the old vehicles like my RX7 I use to drive. When you opened the rooftop, it created a lot of noise because the level of drag is much greater. When I drive my new truck with the rooftop open, there is next to no drag. It does not create so much noise from the wind dragging that I can comfortably talk to my friend who is sitting in my passenger seat.
    For AC, yes it does make a difference. My friend who drove his dodge car, which was very cheap to drive, he immediately noticed the difference it cost to make the same trip he made everyday when he has his AC on during the hot season. The AC draws power from your alternator which can effect the power your vehicle will have. Besides AC air is not the same as fresh air. I know many truckers who swear by never getting sick from breathing the air from the AC instead of just opening up their side window a crack for fresh air.

  • Tony4645

    Premium has already been proven to make no difference on your mileage for you newer vehicles and actually makes your vehicle run worse. They said the only time you would benefit from it is if you are driving an older vehicle that operates with a carburetor because the adjustments, to how lean you want it to burn on fuel, have to be done manually. For all new vehicles that operate with fuel injectors, it makes absolutely no frigging difference because the computer in the vehicle will automatically make adjustments on when it needs more air or less air to burn the fuel the most efficient way and get the most power out of it. When this was proven to be a fact, Shell was sued for making false advertising about premium fuel will give you a better mileage, with more power. I watched this on tv where they hook a car to a computer that read your mileage, horsepower and etcetera with regular and premium fuel and the premium was no better.

    The only time it is important to buy premium is if your are driving any old vehicle with a carburetor or any of your yard tools like your lawnmower, weedeater, chainsaw, snowblower and etcetera because they don’t run with fuel injectors. Plus when they sit too long the ethanol, in regular and mid-grade fuel, will separate from the fuel and create a build up of hard caramel that will make your machine run really bad to the point it won’t start up anymore. I had a mechanic show me a sample of caramel, the size of your thumb. It was all around the fuel filter that was connected to the end of the fuel line and hung down inside the fuel tank, on a chainsaw. He said if you are going to buy ethanol fuel and have it sit for a long time you need to add and additive to it so the fuel won’t separate and it was actually just best to dump the fuel out or just buy premium. The extra two pennies it costs to fill up a chainsaw or lawnmower with premium why would you want to buy regular or mid-grade fuel?

  • Tony4645

    If I can find the video, I will share it with you. It shows right on the video the computer that premium does not give more horsepower to any vehicle with fuel injectors. The drove the vehicle the exact same distance while it was on a machine and the fuel mileage was not better either. They tested how clean the exhaust, coming out the pipe, was and the premium fuel was worse.

  • Tony4645

    Otterdriver I am not going to believe what you say because you don’t drive the same hills, the exact same distance, with the exact same road or weather conditions or the same weight on your truck everyday. Your testing is not going to be as accurate as they did in a shop with the exact same vehicle, that had the exact same weight and many other factors that can alter your mileage and it proved they got the exact same mileage with regular as they did with premium. Like I said on my previous comments, it has already been proven in “COURT” that premium makes no difference when Shell was sued for falsely advertising that premium was better for your vehicle and give you better mileage. If I find the video I will share it with you.

  • Yeah, I seen a video where they measured everything on a computer, with the car on a dyno and there was zero savings or improvement and more emissions. So there is really no benefit to Premium gas. It’s an utter scam really. Also, what people don’t realize is that for regular vehicles, regular gas is better, especially in winter cause it ignites faster than premium. It has a lower flame point than Premium by design. For the huge price difference now between them, I ALWAYS pick regular and never premium. The came has been exposed and it is a total scam. Investigators/Journalist have proven it many times, but when gas execs are interviewed, they deny iy and spout off about the benefits of premium. Lol.

  • Well, point taken and I suppose “some” variables do make a difference. Other do not. As for me, I have a non opening back windshield and no side vent windows, so I know for a fact mine creates drag. I can feel it in the amount I have use the pedal with windows down on the highway. I hear ya though with the AC. Some people cannot stand the stuff and I think fresh air is far healthier. Matter of fact it is no good for your voice box or breathing cause professional singers like Celine Dion or Mariah Carey refuse to stay at places that us AC or where you cannot turn it off yourself, cause it dramatically affects their singing voice. Makes them hoarse. People with serious breathing issues or even non serious ones, say it affects them too. I don’t notice anything, but others refuse to use AC for that reason, so there is something to that notion for sure. You are correct about the AC using more fuel, especially at idle (not so much when running at speed cause the engine/belt is driving the compressor anyway and always running) I heard a mechanic I trusted say it used more fuel and I believe everything that guy says. It makes the biggest difference when idling/city driving.

  • callmebob

    I’m not sure why you’re asking me (?) – did you reply to the wrong guy ?

    I’m of the opinion that there’s really negligible difference myself – I use 88 because it’s what the manual says. I know there were some older engines from pre-2000 that had issues with the initial introduction of ethanol as a portion of the fuel, that that’s long in the past in my mind. I think it’s oversold as an issue personally.

    I get over 40mpg in my 2013 Accord 4 cylinder 4 dr with CVT – I’m good to go…

  • Jonathan A. Wilder

    How so? Efficiency is cost per mile for cars, and fuel consumption is the major variable cost.

  • Zachary Smith

    Efficiency would be the amount of kinetic energy an engine can produce from a set amount of fuel. If you put a Hemi in a 2000lb. car, you would get far better mileage, however, the efficiency would not change.

  • Johnny Drakos

    Bill your statement about “AC will not reduce it nearly as much, because the compressor it is already running off the already running engine.” The AC compressor clutch is not always engaged, regardless weather or not the belt is routed around it, there is no parasitic draw unless the ac clutch is engaged.

  • Jonathan A. Wilder

    Better mileage than what? Generally, larger engines use more fuel, so you would get fewer miles per gallon for the same car with a bigger engine, regardless of its ability to accelerate or its increased top speed. You are being too strict in what you are putting in the numerator of the efficiency ratio. In this context, miles per gallon is efficiency. In another case, which you describe, the derivative “power produced per gallon” would be an appropriate answer. But either way, the more power produced per gallon, the better the fuel economy. Unless you are having fun by flooring it. Then the equation would be dV/d(gallons used).

  • O.k. Cool. That is good to know. I am not an expert in auto mechanics. Still learning, so I appreciate knowing things like that.

  • Zachary Smith

    The efficiency of the engine remains the same. If it is in a larger vehicle it needs to do more work than if it were in a small car.
    We are also back to playing fast and loose with some terms.
    There is no such thing as power produced per gallon. Power is a rate of energy used or produced. Energy would be HP hours or Kilowatt hours.

  • Zachary Smith

    They are sideways because the mechanism takes up less space and is cheaper to make.

  • Ditto_Bird

    Hi folks. I most definitely get at least 50, sometimes more, extra km on a tank of premium versus regular. 2009 Toyota Corolla.

  • ArtieMan

    No you don’t. Your Corolla is designed to operate on 87 octane. The reason for the difference in miles per tank is driving patterns and environmental differences between each fillup. If you understood the science behind how octane works you’d realize how absurd it is to claim you’re getting better fuel economy from using unnecessarily high octane fuel in your vehicle.

  • ArtieMan

    That depends on the brand. This is true of most off-the-shelf “synthetics” but not oils like German Castrol, Motul, and Amsoil.

  • Ditto_Bird

    Thanks, I’ll admit this civil engineer does not understand the finer points of octane ratings. I did of course understand your comments on environmental variables and routes chosen. My experiment, albeit with controls that would not pass rigorous inspection has repeatedly shown me that premium gives me ~50 km travelled. It’s quite a significant difference which I have found to be true time after time.

  • callmebob

    What is the original source of the material used to create the synthetic base oil then ?

    It almost all comes from crude stocks that’s been processed to separate out the various desired CH chains, which are then put back together in formulation to make the “synthesized” oil. ( They put in other additives, but the syn base all comes from crude originally… )

    Lots of steps to get it refined / split into the elements to put back together how they want it, but crude is the source…

  • Jeremiah Bates

    a truck with the tailgate down gets less fuel economy than one with the tailgate up because with the gate up, there’s a low pressure cushion of air produced right behind the cab. if you remove the tailgate and replace it with a net, or lower the tailgate, the low pressure cushion goes away because all the air traveling over the top of the cab drops right into the bed and goes out the back in stead of being reflected up into the vortex that is usually found with the gate closed. I honestly can’t speak on the effects of a tonneau cover because I’ve not explored them

  • True indeed. Good point. You are correct in your thinking about Tonneau covers doing the same thing. They allow air to pass over the truck bed and help fuel economy. Eliminating or drastically reducing drag. The main reason for their invention and they help keep the bed from holding water and preventing premature rusting.

  • george

    Yes, there is. It is called Brake Specific Fuel Consumption, HDFC for short. It tells us how much fuel is used to produce power for a given time. Usually it is stated as pounds per hour per horsepower.
    Any calculation of power always includes a time unit.

  • Zachary Smith

    Well thanks for trying to talk that down to us. If you get any better mileage, it is due to the Placebophonic effect syndrome. 1% better mileage that can be seen only with the Placebophonic effect at the cost of 15% more in fuel cost.

  • Zachary Smith

    The whole thing s a dance engineers must do to align the engine’s sweet spot for the amount of power required to keep the vehicle at it’s designed for at normal cruising speeds. Gearing and torque are also crucial.

  • JohnnyQD

    Contrary to the suggestion made in item 7 of this article, stopping and starting a gasoline engine while in traffic is not a good idea even if it does save fuel.

  • Ted Foureagles

    If that’s true, then something is wrong with your car. I’m not being snarky or dismissive, but added octane just doesn’t have the physical ability to increase fuel efficiency unless your engine is pinging on regular either because it wasn’t designed for regular (your Corolla was) or something is wrong.

  • Ted Foureagles

    With modern fuel-injected cars no. They typically cut off all fuel over certain engine speeds when the throttle is closed. So, if you’re coasting in neutral the engine is still using fuel to hold idle. Of course, road conditions and whether you can coast farther in neutral than in gear play into overall economy.

  • Andrew Land

    It doesn’t SAY that.

  • JohnnyQD

    The article now contains this added paragraph:

    “One should thus turn off the engine when sitting still, except when in
    traffic or waiting in line. New engines start very well and efficiently,
    especially when warmed.”

  • Jason Ingram

    This all said but no one will tell you car manufactures DO NOT program any vehicle for maximum fuel economy or performance.

  • Paul Schwaiger

    The compressor pulley turns when the motor is running the compressor only turns when the ac is on and calls for cooling.

  • Jerry G.

    This article is very good. For any type of vehicle driving habits, and keeping the vehicle well maintained, and not carrying around extra weight (using the vehicle to store things) is key to having better fuel economy. Easy starts, not driving excessively fast, trying to time the speed between lights, proper maintenance, and using the recommended grade of fuel are the basics.

    The weight of your foot on the gas pedal, road conditions, and the weight of the vehicle is a big determination of the amount of fuel you will use when driving. Driving on rough roads, up hills, and through snow will give more resistance, and thus use more fuel.

    With a manual transmission if the driver does not have very good skills how to drive with one most likely more fuel will be used compared to an automatic. Automatic transmissions are computer controlled and should be highly efficient. The CVT would be more efficient because there are no gears. Working with a variable pulley system can have the exact required ratio at any speed. Geared transmissions cannot work with the same precision as a CVT.

  • Tony Bundy

    Some vehicles will benefit. I also have one. YMMV as usual, blanket statements only hold true for most.

  • Rob Storm

    Many cars call for “at least 87” octane, but the fact that it runs on 87 does not mean that it is the most efficient with it.
    Modern cars use computer systems to detect pre-ignition (knock or ping) and adjust timing to eliminate it. Running regular (87 octane) won’t hurt the car, and it’ll run fine, but, if the computer is constantly adjusting timing, you WILL gain mileage and performance by using higher octane fuel.
    Most vehicles, that actually like higher octane, have a notation in the owners manual (or on the label inside the fuel door) saying something along the lines of “for best performance, xx octane is rcommended”.
    If you’re not sure, just try a tank of mid-grade and, if that actually improves things, try premium.

  • Rob Storm

    Actually, TRUE synthetics are not crude based, however, the government made the decision to allow “ultra refined” crude to be classified as synthetic, so it’s very difficult to figure out who is TRULY synthetic, and who isn’t.

  • Mike Labencki

    Premium fuel does not help anything if the compression is under 10:1. This fuel has additives that not only slow the burn but also prevent detonation due to the higher compression. Diesel engines actually rely on this combustion due to compression.

  • callmebob

    People are totally missing the point.
    They want synthetic to be something it’s NOT.

    Even the synthetics are refined, modified and chemically processed (through a number of steps) from elements which were almost exclusively originally crude…

    Now about 2-ish years ago some started being made from natural gas stocks instead, because they could control the molecule sizes easier due to the starting component purity – not having to overcome weeding out what was originally varies sizes in crude… so that’s a relatively recent variation.

    They don’t just pull synthetic elements in these oils from the air, they come from various steps of processing what used to be almost exclusively crude, the recent NG origin changes it some. Haven’t chatted that approach over with the ChemE buddy in Houston yet – we only touch base a couple times a year or so.

  • Johnny Payne

    I seem to be the only one that I know, that puts their automatic transmission in neutral every time I stop. the reason I do this is they put a neutral on it for a reason. Transmission left in drive while stopped is still working. Save wear and tear by using neutral

  • Mr. Odain

    No, you are not the only one. I also always go into N while idling. Not only does it save on transmission, but also brakes

  • Johnny Payne

    I’m glad I’m not the only one. Had not thought of brakes. It just makes since to use neutral to me especially for transmission sake.

  • Find the ideal speeds you’ll do even better. Most engines have sweets spots that will get you that extra mile. Per 45l tank, My 15 year old 01 sunfire could get 800+ km at 90. 450 at 110. 400 at 50.
    It did better than my 7 year old matrix does <350km on 45l at 50kph

  • Trevor

    Three pedals and a shifter at the right hand. Hard to get more efficient than that if you know what you are doing. EPA ratings on my newest MT ride are a joke. Trending 15-20% more than the EPA combined cycle. Plus with all appendages engaged zero risk of texting, knee steering, etc. Back to basics. We are driving not aiming.

  • James Fenerty

    When you slow your car down and the engine gets below a certain speed, the torque converter no longer has enough fluid shearing going on to continue providing direct output to the transmission. It is designed to allow this to happen. Your transmission will not suffer any adverse effects by allowing it to happen. No additional wear occurs because of this.

    Consequently, by shifting out of gear at stop lights, you are creating excessively more wear-n-tear on your transmission/shifter/linkage than would otherwise exist by just leaving it in gear.

  • Daniel Isbell

    The primary reason that modern automatics (with traditional torque converters) are now being advertised as having better fuel economy than manuals in the same car is that the manual transmissions are being built with closer gear ratios. The automatics are set up ideally for highway use, but the manuals are designed to feel sportier at the expense of fuel efficiency. If manufacturers offered both with similar gear ratios, the manuals would still be getting better EPA ratings. CVTs & dual clutch automatics on the other hand do have benefits that will often make them actually more efficient than an equivalent manual.

  • Stacy Shirley

    why would it save on brakes….your not moving so there is no brake wear

  • Stacy Shirley

    efficiency is how much of the energy in the gasoline that actually gets converted to usable power.it relates to mileage only because higher efficiency engine tend to get better fuel mileage

  • Christopher Holman

    I don’t shift into neutral for idle unless its going to be an extended time sitting still – traffic jammed, drive thrus. Consider also the extra wear on shift linkages to even do such.

  • Hugues Merone

    back then the automatic transmission was heavier so you couldn’t achieve a good fuel economy
    I remember when I work for a honda dealer they told me and I checked the automatic version for the fit second generation came without spare tire to save weight compare to the manual version