Home Rental Cars What To Do If You Put The Wrong Octane Gas In Your Rental Car

What To Do If You Put The Wrong Octane Gas In Your Rental Car

by SharonKurheg

Every car has a recommended type (octane) of gasoline, commonly known in the U.S. as Regular, Mid-Grade (or Plus) and Premium. Well, there’s diesel too but fortunately, diesel pumps don’t fit into non-diesel gas tank openings in the U.S. Most rental cars work best on regular gas (87 octane), which is good because regular gas is always cheaper than mid-grade and premium ;-).

However, there are a few rental cars that require Premium or, on rare occasion, diesel (either way, the car rental company should tell you when you pick up the car). And if you rent a car outside the U.S., all bets are off in terms of color coding their pumps the same way they do in the U.S., or even if the diesel pump will or will not fit in your rental car’s regular gas tank opening. So it may be easier than you think to put diesel into a car that needs regular, or regular/mid-grade into a car that needs premium or diesel.

But here’s what to do if it happens to you (thanks to Autoslash for these suggestions):

  1. The first “what to do” is actually what NOT to do. Don’t start the car. Once the car is started, the inappropriate gasoline gets into the works and will cost a whole lot of money to fix. If it’s never started, the gas just sits in the tank. Draining the tank isn’t cheap by any means, but it’s still cheaper than having to clean everything in the entire engine.
  2. Put the car into neutral and move the car so it’s somewhere safe while you do what you have to do to get through this mess (and yes, that may include crying; we won’t judge).
  3. Here’s the embarrassing part. Call the rental car company and let them know. I know, I know, it’s like the time you were playing basketball inside the house when your mother wasn’t home, tried to dunk into the garbage can, missed, and the basketball fell down the stairs and broke your mother’s favorite vase. And mom always said don’t play ball in the house. But you had to tell her. And you have to let the car rental company know. Make sure to specifically say you put the wrong kind of fuel in it, but have not started the car (Well, unless you did. More on that in a minute).
  4. Ask the rental car company where they want you to bring the car. But don’t drive it there! (remember, you’re not supposed to start the car) Instead…
  5. Call roadside assistance. Hopefully, you have your own. Let them know that you need to have the car towed. Realize that you’ll be paying for this per mile.

Whatever the rental car company says to do, do it. Don’t pick a place to get it fixed – that’s the rental car company’s decision. And honestly, if you wind up bringing it to a place they don’t recommend, that’s a violation of your rental agreement, which could put you on the “Do Not Rent” list – you’ll be deemed a risk and they (and any sister car companies) could potentially never rent to you again. You don’t want that.


But what if you didn’t notice you put the wrong gas in and already started driving the car? Symptoms of putting the wrong kind of gas in the tank include erratic acceleration, misfiring, and excessive smoke from the exhaust. Here’s what to do if that’s what you’re experiencing right after putting gas in the car:

  1. Stop driving the car. Pull over to a safe place and just…stop.
  2. Take the key out of the ignition. Leaving the car running, even if you’re not moving, will mess up the entire engine.
  3. From here on in, follow Steps 3, 4 and 5 from above. Let them know, find out where they want you to bring it, and call roadside assistance to have you towed.

The bottom line is, you need to be VERY careful about making sure to put the correct type of gas into your rental car’s tank, because that’s the type of human error that your insurance probably won’t cover – and it’s an error that, between the rental car’s loss-of-use fee (they can’t rent the car while it’s being fixed), repairs and administrative fees, could wind up costing a small fortune. So just be REALLY careful, OK?

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This post first appeared on Your Mileage May Vary



Steven December 8, 2021 - 9:29 am

Modern cars have knock sensors and you won’t notice anything if you put the wrong grade of gas in the car. Maybe a little less power.

Courtney December 8, 2021 - 9:49 am

Uh, unless you inadvertently put diesel in a gas or vice versa, I’m not sure this is much of an issue.

I’ve never had problems in my own cars of occasionally using a different octane… it’s definitely not something to do consistency.

Dan December 8, 2021 - 10:37 am

While a gas/diesel mix up is serious and can run into serious issues, an octane mix up is far less so. If you only put a few gallons of 87 into a car requiring premium, it will likely only drop the total octane a point or so. Usually, cars like that usually ask for 91+ octane. So a calculated octane of 91 or 92 is just fine. Unless the car is being driven aggressively, even dipping below 91 octane is very unlikely to have serious affects long-term, unless it is constantly being run with lower octane. Cars can detect the lower octane and adjust themselves to reduce knock. Moral of the story, try not to use the wrong fuel, but it’s not the end of the world and pumping the tank is not necessary.

stogieguy7 December 8, 2021 - 10:46 am

Uh, I think that author is confusing the concept of “octane” with the actual type of fuel. If you put regular into a vehicle that requires premium (such as one with a turbocharger), this will result in decreased performance and may even decrease your MPGs. Aside from that, one tank of gas isn’t going to do any damage – unless you tell the rental car company and they decide to extort money out of you for “repairs” that aren’t actually required.

Now, foolishly putting diesel fuel into a gasoline powered car (or vice versa) is an entirely different matter and the author’s advice is correct in this case. However, doing this has NOTHING to do with octane.


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