It’s an age-old question, and the result vary wildly case to case. Though this is a surprisingly common mistake, it’s important to be mindful of what type of fuel your vehicle requires, and what type of fuel you’re putting into your car. If you accidentally put the wrong fuel type in your vehicle, KB Motorsports can give you a good idea of what to expect:
Putting Diesel in a Gas Car
Diesel fuel nozzles tend to differ from regular gas nozzles at a gas station, so this mix-up is a bit hard to make—but mistakes do happen. If you realize you’ve made the mix-up, stop driving the car. Parking and turning the car off will help to limit the damage. Otherwise, the car will eventually use up the gas in the tank and eventually shut down, since regular gas engines cannot combust diesel.
The best thing to do is to drain the tank, fuel lines, fuel rails, and injectors. You can attempt this yourself, but it’s best to trust this type of job to a professional.
Putting Gas in a Diesel Car
This mix-up is far more dangerous for your vehicle. Diesel not only acts as vehicle fuel, but as a lubricant as well. Putting regular gas into a diesel vehicle can really damage the fuel injector pump. Diesel and regular gas also have different combustion properties; regular gas will detonate much earlier than diesel, which will result in misfires and knocking that will require you to have parts of the engine repaired, rebuilt, or even replaced.
Putting E85 in a Gas Car
At some gas stations, you’ll find some pumps labeled as “E85,” which means that the fuel has a much higher blend of ethanol. Cars that are labeled as flex-fuel can switch between this type of gas and regular gasoline without issue, but if your car is not flex-fuel, you might notice some issues.
The check engine light will most likely illuminate, but you can top off the rest of your tank with regular gasoline and ride it out. A one-time mix-up with E85 gas shouldn’t cause any long-term damage.
Putting Premium Fuel in a Car That Doesn’t Require it
Though you might assume that this sort of mistake could cause major issues, it’s quite the opposite. If you accidentally put premium fuel into your regular gas car, nothing significant will happen.
Putting Regular Fuel in a Car That Requires Premium
This mistake is a different story. Using lower octane fuel in a vehicle that requires premium gas could cause some serious internal damage. You’ll most likely notice the spark knock (a sort of high-pitched pinging or rattling noise). Luckily, the engine computers can adjust the timing to limit the amount of damage caused, but you’ll notice lower fuel economy and reduced performance in your vehicle.