Do Engine Start-Stop Systems Actually Help You Save Gas?

Do Engine Start-Stop Systems Actually Help You Save Gas?

Many new cars come with automatic engine start-stop. These systems are designed to save the fuel wasted at idle by turning the engine off when you come to a stop.

These systems are becoming more and more common in cars and trucks. Even the Ford F-150 is arriving with this system as standard equipment, promising more MPGs.

But the fuel spent during idle seems insignificant, right? Even the EPA’s fuel economy tests seem to downplay the significance of these systems. How much fuel can really be saved, and can everyone benefit from this technology, even if they spend most of their commute on the highway?

Here’s how it works for the driver: When you come to a stop, like you would at an intersection and hold the brake while you wait for the light to turn green, the engine will shut off. On cars with manual transmissions, you usually have to put the car into neutral in order for the engine to shut off. As soon as you let off the brake or engage the clutch, the engine will automatically and quickly fire up, so you can get on your way again. These frequent restarts require a different starter motor that’s more robust and paired to a different, tougher battery.

ALSO SEE: GM Adding Start-Stop to Nearly All Models by 2020

Furthermore, unlike when you turn off your car entirely, the rest of your car’s features will remain on even if engine start-stop system is active. That means you still get A/C, radio, navigation and all that. A bigger battery helps with that, and some cars even feature an extra battery or a super capacitor.

Still, despite updates to the new five-cycle EPA test, it may be hard to see the tangible benefits of an engine start-stop system.


“The engine idle duration for this test is fairly representative,” explains Thomas Recke, a PR specialist for Continental Automotive. Continental is an automotive supplier that provides engine start-stop technology to automakers. “However, the idle time is stressed with extreme temperatures: the A/C test cycle exposes the engine to 95°F, whereas the cold city test is performed at 20°F. The engine must remain on in order to provide climate control.” This helps to explain the unimpressive EPA ratings of cars with engine start-stop.

It also helps to point out that the effectiveness of engine start-stop systems can fluctuate for a number of reasons.

“Fuel savings will vary depending on the type of start-stop system, driving style and driving cycle,” explained Recke. “The average U.S. driver with a basic system will save around 4 percent.” He also explained that more advanced systems, like those used in mild or full hybrids, can improve savings even more.

A 4 percent improvement in fuel economy isn’t too shabby, but Recke pointed out that can change drastically based on what kind of driver you are and the type of commute you have. A city driver, for example, who can spend about a quarter of their drive time stuck idling in traffic can see an improvement up to 8 percent by driving a car with an engine start-stop system. On the other hand, aggressive drivers who roll through their stops or drivers who spend much of their time on the highway will see less of an improvement on their fuel consumption.


“Eliminating rolling stops as well as creeping after engine stop will help maximizing the fuel savings,” explains Recke. “Additionally, reducing the A/C and heat will help.” He pointed out that most new cars have automatic controls that reduce A/C and heat automatically when the engine is turned off.

“The most important step to maximize benefits is to drive normally,” explains Ulrich Muehleisen, head of marketing and product development for starters and generators at Robert Bosch LLC. Bosch is another automotive supplier that provides engine start-stop systems. “When the system is active, any full stop will start providing immediate benefits. The biggest impact will be from the system activating regularly during normal driving.”

Interestingly enough, while there’s a decent impact at the pumps, your wallet may be suffering in different ways. Powering this new technology are advanced batteries. “Start-stop batteries are put under more load than a normal battery,” said Muehleisen. “So every OEM has taken steps to strengthen and protect the batteries. All OEMs have implemented battery monitoring systems. Almost all OEMs have upgraded their start/stop batteries, which are capable of handling the extra cycling.”

Muehleisen pointed out that these batteries still meet all the same durability requirements as traditional batteries, while still offering the extra juice to handle start-stop responsibilities. “Since these batteries are not mainstream quite yet, they are a little more expensive, but should be easy to find,” he said.


It’s clear that there are some benefits with these systems, but it may depend completely on how you drive. If you think you’re spending too much of your commute idling, then you can probably earn a few MPGs by owning a car with engine start-stop. But don’t forget that the extra load on the battery may cause it to wear out sooner, and it may be more expensive to replace.

  • smartacus

    i am of the persuasion that lowering idle to 300-500 RPM will supplant micro-hybrids in the future. Specifically because turbos and start-stop do not naturally mix.
    Difference in fuel usage between zero RPM and 300-500 is so minimal as to not warrant the extra weight, complexity, and cost of a start-stop MHD system.

    This is before factoring in turbo oil/coolant circulators, and air conditioners that need to be designed to run independently of the engine.

    Not to mention; start-stop is routinely overridden, defeating its own raison d’être.

    Now 600RPM and below is idling rough, so there will have to be something to smoothen power pulses.

    The answer is a tag-team matchup of ultra-low-lift/duration capable valvetrain and a small cordless drill motor with a max speed of 700 RPM, which would be enough of a helper. The electricity to run the drill motor could be readily be supplied by the car’s battery or by a compact and lightweight cordless drill battery that is easily rechargeable/replaceable (think Black And Decker)

    here are a few more benefits i can think of just off the top of my head:
    -Less strain on the dedicated starter motor if it’s working in conjunction with the helper motor
    -Starting the engine at much lower RPM

    -Helper motor can assist the engine during very low RPM bottom-torque, like when rolling off from a stop
    -Resulting in less stress on manual’s clutch surface when engaging from a dead stop
    -Zero throttle input during Dead Stop roll-off clutch engagements will be much more frequent

    -Automatics will generate less heat in their torque converters during stall/idle
    -Torque converter can be designed much harder (read much lower stall) improving efficiency

    -Ability to creep forward in traffic at much lower speed without stalling or riding the brakes

  • earl

    wish these systems were an option, rather than showing up on more and more models. I for one, don’t want one and bought a new car last year before all cars end up with them.
    I don’t like the momentary hesitation, I don’t need the anxiety of it not starting, I don’t need the extra battery or cost of the complexity. I don’t need the expense of a new starter down the road as long term reliability is unknown. I don’t want to have to turn off the system every time I get in the car.
    If I want to save 2%, I drive and brake conservatively and/or buy a slightly smaller car.

  • Jeffery Surratt

    I agree. If your car gets 25 mpg and you get a 4% savings = 1 mpg. This saves you $72 @ $3 per gallon in 15,000 miles. I will not be buying any vehicle with this system.
    Beefed up starter $200+, install $200, heavy duty battery 3 to 4 times what a regular battery costs. Stuck on the side of the road, when system fails. Loss of car for repairs???. Not worth it, for maybe a savings of $480 in 100,000 miles.

  • Henry Rose

    No mention of reduction in emissions! If 4% or even 1% fewer people die from air pollution – and don’t think emissions aren’t a huge health problem – then the technology is worth it. Full hybrids are better and pure electric (in certain states and provinces) even better.

  • Diesel Driver

    You have no idea how freaking bad lithium ion batteries are, both to manufacture and to recycle. They’re horrible. All you are doing with a battery powered or partially powered car is moving the pollution to whatever factory is building and recycling the batteries and to the power plants that recharge the all electric cars. You lose over 50% of the power generated at a power plant getting it to the end user. Plus there’s a lot of places where you CAN’T let the engine turn off or you’ll roast or freeze do to outside conditions. Most of Arizona and much of southern California, New Mexico, Texas, all of the southern states get freaking hot for 3 to 5 months of the year, out here in the west it stays over 100 degrees every single day, for a couple of months each summer.

  • Diesel Driver

    My parents bought a brand new 1967 Pontiac (only new car I ever remember them having) and the owner’s manual said it used 1/2 a gallon of gas if it idled for an hour. That was with a 389 4 barrel carb engine. If a 2 liter engine uses over 1/4 gallon in an hour then I think something is wrong with it. Plus I want to know how they keep the A/C running like it said in the article “That means you still get A/C,”? Only 2 ways I can think of, having the engine stay running (no fuel savings) or drive the a/c compressor with an electric motor, which will put additional load on the battery and increase the weight and complications of the normally engine driven accessories. It takes power to recharge the battery each time the engine stops too. Plus if you take a half second to start moving again after the light turns green people start honking. If I ever end up with one of these cars I’m going to find a way to disable that “feature”.

  • Diesel Driver

    Or you could just add a heavier flywheel.

  • Riggs DeMurtaugh

    The rental I’m currently driving has this feature. It’s a 2016 Jeep Grand Cherokee. It only shuts off once you’re stopped for at least a second. Then it pretty much starts instantly, like if I start to let the brake pedal go to start moving, it’ll be fully started and ready to go by the time my foot gets to the gas.

    I also found that once it restarts, like say I’m four or five cars back at a red light, if I start to inch forward and stop again, it doesn’t turn back off.

  • I realize this topic is about 1 year old. But we’ve grown concern with several new vehicles being forced to equipped this system. Our main draw the 2018 & 2019 Jeep Wrangler JL & JT (Truck). According to our sources, the new Jeep will have three engine choices, which two of these engines would be equipped with the ESS system. Let me remind everyone that “Jeep” or those who drive them will not tolerate the Wrangler to have the ESS system in these vehicles. The main reason is because a large number of these jeepers tend to take their jeeps off road and if Jeep is forced to install these systems in their new Wrangler. These jeeps would be obsolete for off roading. Clearly another attempt to force consumers to drive with limits as set by the government etc. There are a few things in life one simply does not mess with.. and The Jeep Wrangler or Off Roading falls into this category. Do not attempted to take away our freedom of off roading. In this light, I may have found a flaw in the system, However I need someone to test any vehcile which has been deems off road capable and has this ESS system installed. I’m mainly interested in the feed back or any inconsistence that may occur while driving off road.

  • Over night, a few Jeepers have stepped forward offering a bit more about off roading with the ESS system installed on their jeeps. They all claim/say that the ESS system is disabled when the 4 wheel drive is engaged. Although this sounds hopeful and promising.. the fact of the mater is that even if we’re not off roading.. the ESS can be annoying with it’s lack of response and slight hesitation. Clearly the interested consumer has not been informed of this “laggy” system which is evident by the amount of Jeep grand Cherokees on any given used car lot.. In our Area, We’ve counted at least 32 on one lot and approx the same amount of slightly less on surrounding used car lots. Even though we’ve been searching for all Jeep products which have the ESS system installed.. Other vehicles are ending up on the lot as well due to this laggy/hesitation which has been integrated into Hybrid cars and trucks. One either likes it or hates it.. We just happen to be one of those that hates this system and will continue to strive to find a cure in being able to disable this system completely.