Ask a Technician: What Would Happen if I Put Diesel Gas in My Regular Engine?

Q. What should I do if I wasn’t paying attention at the gas pump and put diesel fuel in my tank and my car does not have a diesel engine?

A. Uh-oh. First things first. Do not start the engine. The worst thing you can do is start your car and draw the diesel fuel into your engine. Don’t panic--and definitely don’t put the keys in the ignition.

While both regular gasoline and diesel fuel come from crude oil (petroleum), diesel is an entirely different type of fuel. Diesel fuel is thick and oily-- so oily that it’s often called diesel oil.

While regular gas is designed to ignite with the addition of a spark (from your spark plug), diesel fuel is designed to self-ignite under compression. Diesel is much denser and can really gum up the inner-workings of your gas engine. Imagine thick, gooey molasses-like stuff clogging up your engine. This is why your first move should be a call to a tow truck.

If you do turn on your engine and draw the diesel into the engine, filters, carburetor or fuel injection system, you’re going to have a hefty repair bill. The entire engine will have to be cleansed, which is no cheap endeavor.

Worse than filling your gas tank with diesel is doing the reverse. If you have a car that takes diesel fuel and accidentally fill it up with regular gas, you’re in for a world of hurt. In both scenarios, the best thing to do is call a tow truck and have a professional take care of the problem.