Putting the wrong type of fuel in your car is a common mistake that might send you into panic mode. However, whether it damages your car or not depends on two main factors:

Fuel type: Commonly includes regular gas with an octane rating of 87, midgrade at 89, and premium gas at 91 or 93, diesel, and E85 or flex fuel.
Vehicle: Most cars run on regular gas, while others may require premium fuel only or have a recommended octane level, usually indicated on the gas cap. Diesel fuel is only meant for vehicles with diesel engines, while E85 is for flex-fuel automobiles.

Keep reading for possible scenarios and learn what you should do if you put the wrong gas in your car.

Does Premium Fuel Make Your Car Run Better?

Some drivers swear that using a higher-octane fuel is better for a car’s performance, but it’s not. Engine computers can usually adjust their timing to account for the increased octane levels, so if you put premium gas in a regular car, you probably won’t notice anything. However, some engines are not designed to burn higher-octane fuel, and you may see a reduction in performance and fuel economy.

What If You Use Regular Gas in a Premium Car?

Engine computers can adjust the ignition system to accommodate lower-octane fuel — to a point. If you put lower-octane fuel into your high-octane vehicle, whether by mistake or to save money on gas, you’ll probably notice the effects right away: things like poor fuel economy, reduced acceleration, and spark knock, which sounds like a high-pitched pinging or rattling noise.

A one-time slip-up likely won’t lead to major damage, but you shouldn’t make a habit out of it.
Refer to your owner’s manual. If the vehicle manufacturer says the engine requires premium gas, take their word for it, and don’t put 87 instead of 93 in.
Don’t try to save a few pennies per gallon by using regular gasoline, or you could be in for expensive repercussions.

What Should You Do If You Put E85 in a Gas Car?

E85 (or flex fuel) is a type of fuel that contains a higher concentration of ethanol. Many flex-fuel vehicles (FFVs) can use both E85 and unleaded gas without any problems, but if you accidentally fill your non-FFV with E85, you could be in for an issue.

If you’re still filling up at the pump and realize your mistake, you can top off the rest of your tank with regular gas.
Your check engine light will probably turn on, but it will turn off once the fuel starts to burn off.
If you don’t realize your mistake until later, continue to periodically top off the tank with regular gas as you drive around and burn fuel.

Luckily, a one-time mishap usually doesn't lead to any long-term damage or expensive maintenance.

What Happens If You Put Gas in a Diesel Car?

Burning gasoline in any diesel engine will likely cause irreversible damage, and in newer clean diesel vehicles, any amount of gas will damage the vehicle’s emissions controls. By putting gas in a diesel car, you can do a lot of damage to the vehicle’s fuel injector pump. Additionally, gas combusts much faster in a diesel engine which can lead to misfires and knocking, requiring certain engine parts to be repaired, rebuilt, or replaced.

If you realize you accidentally put gas in a diesel-powered car, park and turn your vehicle off as soon as you realize your mistake. Any more driving will rack up the repair bill.
Have your vehicle towed to a mechanic who can thoroughly flush your gas tank and fuel lines.

What Happens If You Put Diesel Fuel in a Gas Car?

The gas and diesel nozzles at the gas station look different, so it’s difficult to mix them up. However, accidents happen, and there are crucial steps to follow if you realize you accidentally put diesel in your car.

Once your tank runs out of any remaining gasoline, your engine will shut off because it is not designed to burn diesel fuel.
If you put diesel in your gas engine, park and turn off your car as soon as you realize your mistake to prevent further damage to your engine.
You’ll need to drain your gas tank and fuel lines, which is a job best left for a mechanic. Contact a towing service or Roadside Assistance for a tow to the nearest mechanic.

Coverage for Wherever the Road Takes You

Putting diesel in a gas car usually doesn’t cause lasting damage, but it can be an expensive mistake. A mechanic might charge anywhere from $500 to $1,000 to drain your car of diesel, plus the cost of a tow.

Fortunately, having Roadside Assistance could help you save money by covering the cost of the tow! Review your car insurance policy to see how you’re covered. Direct Auto can help you get affordable auto insurance with Roadside Assistance coverage. To learn more and for a free quote on car insurance, call 1-877-GO-DIRECT (1-877-463-4732) or come into a Direct Auto location near you.

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