What Happens If You Put the Wrong Fuel in Your Car?

What Happens If You Put the Wrong Fuel in Your Car?

Does your car need regular fuel or premium? Gas or diesel? What happens if you put the wrong fuel into your car?

The results vary wildly from case to case, but you need to be careful about what kind of fuel you put in your car and be aware of what effects your actions might have. Putting the wrong fuel in your car is a surprisingly common mistake that no one ever wants to admit to, but don’t worry, we have your back.

What Happens When You Put Diesel in a Gas Car?


Due to the different types of nozzles used for gas and diesel fuel at stations, its usually kind of difficult to mix them up, but mistakes do happen. If you realized your mistake, the important thing is to stop driving the car. Parking and turning off the engine will limit the damage that will occur. Otherwise, the car will use up the remainder of the gas in the tank and eventually shut down, since gas engines can’t combust diesel.

What you need to do is drain the tank and fuel lines, fuel rails and injectors of the diesel fuel. You can try to do this yourself, but a mechanic will be better suited to handle this kind of work. Usually, there’s no permanent damage, but this kind of fix can cost anywhere between $500 and $1,000 plus the cost of a tow to the closest mechanic.

What Happens When You Put Gas in a Diesel Car?


Going the other way around is far more harmful and dangerous for your car. Diesel is not only a fuel, but serves as a lubricant as well, so you can really damage the fuel-injector pump by using gasoline instead of diesel.

That’s not the only thing that can go wrong. Diesel and gasoline have different combustion properties, meaning that gas would detonate much earlier in a diesel engine. As a result, you’ll get misfires and knocking that will require certain parts of the engine to be repaired, rebuilt or replaced, which will be expensive.

If you discovered that you accidentally put diesel into your gas-powered car, you need to stop running the engine immediately and get a tow to a mechanic, where they will drain and clean your system.

ALSO SEE: Do I Really Need Premium Gas?

What Happens When You Put E85 in a Gasoline Car?


Some pumps are labeled as E85. E85 is a fuel that has a much higher blend of ethanol. Some cars, labelled as flex-fuel vehicles or FFV can switch between E85 and normal pump gas without any issues, but if you accidentally fill your non-FFV car with E85, you may notice some issues.

For starters, you’d at least get a check engine light, but you can top off the rest of your tank with regular gas and ride it out. “One time misfueling should not cause any long-term damage,” said Robert White, vice-president of industry relations at the renewable fuels association. “Even that light will cycle off once the fuel mixture issue has been resolved.” He also pointed out that “accidentally fueling with extra ethanol is not like a diesel misfueling that automatically shuts down the vehicle, requires service and expensive maintenance. Consumers are usually able to navigate the issue with little issue, and the number of calls we get has dropped tremendously over the years.”

So if you’ve accidentally put E85 into your gas car, top it up with regular gas a few times and ride it out.

What Happens When You Put Premium Fuel in a Car that Doesn’t Need It?

Octane Art

Some people think that using Premium in a vehicle that doesn’t need it will turn their car into an asphalt-eating monster. Sorry to burst your bubble, but nothing significant will happen. In some cases, like while towing or in hot, dry weather you might see a slight benefit, but due to the engine computers adjusting their timing automatically to compensate for the increased octane levels, no damage or noticeable benefits will occur.

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

What Happens When You Put Regular Gas in a Car that Needs Premium?

On the other hand, using lower octane fuel in a car that calls for premium can cause some serious internal damage. You’ll likely notice the spark knock, which is best described as a sort of a high-pitched pinging or rattling noise. Fortunately, the engine computers can adjust timing to limit the amount of damage caused, but you’ll definitely notice reduced performance and worse fuel economy. Switch back to premium fuel as soon as you can, because all that spark knock can cause long-term damage.

  • Jonny_Vancouver

    Good article.

  • Wilmington

    “…..the car will use up the remainder of the gas in the tank and eventually shut down, since gas engines can’t combust diesel…….”

    I had expected the gas would rise to the top because it is lighter , or perhaps even mix-up. But the gas staying at the bottom of the tank is a surprise to me. Does anyone know why it would stay at the bottom ?

  • I Am Not A Mechanic™, but my wild guess would be that it’s gas that’s already been drawn into the lines by the fuel pump.

  • Bryan Fullerton

    Actually that’s just fiction. The writer has no clue what he is talking about. Gas and diesel will mix. But just like the rest of that part of the article it all depends on how much of which got mixed.
    I run diesels and I was young when my granddads new diesel van got gas put in the tank by the clueless gas station attendant(oregon you can’t pump your own gas). My mother was driving it at the time and it probably had 1/4 of a tank of diesel. It rattled pretty loud. They replaced the injection pump despite the fact that it was still working fine because it easily could have been damaged that would have shown up later. Personally had It been mine at the time I would have kept the old pump and tore it down to see.
    As for diesel in a gas engine I can thank my little brother for showing us what happens when you do that. He fueled up our old gas Volvo with diesel. Basically as long as it was hot it would run. Not run well mind you but would run. It smoked white smoke all over the place but it still ran till he saw the smoke and parked it. When I got there it had cooled down some and really didn’t want to run. I think I got it started and made him drive it home but I may have towed him.
    Now this is where it gets interesting. We siphoned that gas diesel mix out of the tank and replaced it with gas. As an experiment we heavily diluted (probably 10%) that gas diesel mix down with gas and ran it in my dads 460 ford powered van. It drove him nuts because it wanted to ping pretty heavy. He had to retard the timing till that tank was all used up.
    (Our family is composed of teachers and mechanics with my dad being both)

  • Cobranut

    Great info Bryan.

    The reason for the knocking is that diesel has extremely low octane, it is made to detonate, as that’s the normal mode of operation for a diesel engine. It can quickly knock a gas engine to death if you were to keep driving it like that.

    Back when I was very young I worked for my Dad, repairing power equipment.
    A guy brought in a push mower that he said ran fine the last time he used it, but wouldn’t start now.
    I checked that it had fuel, pulled the rope a few times and nothing. I checked for spark, then used a shot of ether and it fired briefly. After a couple more shots it started and ran, but was smoking white smoke, which went away as it warmed up. It also smelled odd.
    Turns out, he last time he mowed he had fueled it with kerosene. It started up while warm, but after it cooled off it wouldn’t fire. LOL

    Dad told me of old tractors that had a small gas tank in addition to the main kerosene tank. During the war gasoline was scarce, so they’d start the tractor on gasoline, then switch to kerosene once warmed up. Then they’d switch back to gas a couple minutes before shutting it off so it would start again next time. 😉

  • Bryan Fullerton

    Yep and the diesel can better handle knocking but it is still not good for it.
    DEid your dad tell you about the tractors during the war and how they powered them? No gasoline or diesel or kerosene. They ran the tractors on wood smoke. A few people still build those gasifiers today and there is tons of howto info on the internet about it. Our granddads and great grandads were quite ingenious it seems.

  • Cobranut

    Bryan: Interesting, I don’t recall Dad ever mentioning those, I did a bit of reading on them, and I agree, those old farmers were pretty resourceful when it comes down to making do with what they had.

  • Corey Stevens

    This man speaks the truth the two gases will if the mixture is too concentrated of diesel it will not burn if it is not it will burn but your car will smoke a lot . know that you’re probably going to get pulled over for visual emissions. The best thing you can do here is to siphon out as much gas as possible and then putting more gasoline but not a whole lot just enough to get the car to run again. Then you’re going to have to let that car idle until the tank is empty and there’s going to be a of smoke . You’re probably going to want to get your fuel injectors cleaned afterwards.


    I put regular gas in this HHR and didn’t realize that it said e85 I only put 10 dollars in and the heck engine light came on.what can I do?help

  • MichaelZWilliamson

    Just refuel with proper fuel and keep driving. it will settle out in a few miles.

  • Jimbo99

    With using 87 octane in a car that requires 91 or better, maybe you could aleways just pour in an octane booster product from Wal-Mart or wherever ?

  • Nathan Tiessen

    Can confirm; author is a content writer and not a car guy.

    Regular 87 octane gas in any new vehicle that recommends 91 octane gas just means that the knock sensors will automatically retard the timing to avoid predetonation. I’ve run 87 in my German car that calls for 91 for years.

    Regular 87 in an older high compression vehicle without a knock sensor will kill it, though. My ’87 Honda Super Magna bike is not happy on anything less than 94 octane.