What Happens If I Put Diesel Fuel In A Gas Car?

Filling up with the wrong type of fuel can be a costly mistake.

Fuel pumps at a gas stationShutterstock

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We've all heard stories about someone putting diesel fuel in their gasoline-powered car, but have you ever learned what happens after? Or what it might cost to repair the fuel system or engine once contaminated? And how does a mistake like this happen in the first place? We'll answer all of these questions as we find out what happens when you put diesel fuel in a gas car.

What Happens If You Put Diesel In Your Gas Car?

If you do manage to put diesel fuel in your gas car a number of things could happen to your car's fuel system. The good news is that diesel fuel probably won’t destroy your engine, though it may require replacing some parts.

The problems you face will depend on how much diesel is in your tank, especially in relation to how much gasoline was already there. If you had a nearly full tank of gasoline, for example, and added a gallon or two of diesel fuel on top, it might not be as big a problem as it would be if you filled an empty tank with diesel.

While there will be a wide range of problems for individual cars and your individual situation, most cars with a small proportion of diesel mixed into their gasoline may still run and drive, but they will exhibit symptoms like difficulty starting, reduced power, emitting smoke from the exhaust, and potentially causing the catalytic converters to fail due to the excess unburnt fuel and particulates the diesel leaves in the exhaust. If a larger proportion of diesel is introduced to the gasoline car's fuel tank, it won't start at all due to diesel's different combustion properties.

How Much Will It Cost To Fix?

The cost to fix a gasoline car that's been filled with diesel fuel will vary widely depending on your mechanic labor rates, the type of car affected (e.g. luxury cars are more expensive to fix), and the severity of the problem. It could cost as little as a few hundred dollars to–essentially the cost of a tow to a local mechanic and then the fee for draining the tank and flushing the fuel system–or it could cost thousands if parts like fuel injectors, the fuel pump, or catalytic converters need to be replaced.

How To Avoid Putting Diesel In A Gas Car

Because putting the wrong type of fuel in any vehicle–diesel, gasoline, or other–is typically a time-consuming and potentially expensive problem, gas stations take precautions to help keep it from happening. The primary way gas stations keep diesel out of gasoline vehicles is making the filler nozzle too large for a gasoline car’s fuel filler. Another way gas stations avoid confusion between fuel types is to color the handle green. Not every station follows this rule, but many do.

Even if the nozzle won't fit into a gas car and the pump handle is green, it's still possible to accidentally put diesel into your gasoline car. One possible way would be to fill up a fuel can with diesel by mistake, then pour it from the can into your car. So perhaps the most important thing you can do to avoid putting diesel in your gas car is to pay close attention.

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Nelson Ireson
Nelson Ireson is a car writer, photographer, and editor with 15 years of experience in the fast-paced world of online automotive news, reviews, and video production. Nelson’s passion is driving the latest in luxury and performance cars, translating his experience behind the wheel into words, emotions, and enthusiasm.