Ask a Technician: What Would Happen If I Put Diesel Fuel in a Regular Car?

Short answer: you'd be in trouble

If you're an absent-minded driver, or if you're just in a hurry, one of the biggest mistakes you could make is to put diesel fuel into a regular Lynch Ford Chevrolet car. It probably seems easily done, particularly in gas stations where different types of fuel come from the same pump, but if you were to make this mistake, it could prove very costly.

Simply put, a gas tank filled with diesel simply won't start. The fuel injectors in the engine would inject the diesel fuel into the engine's cylinders, but when the spark plugs fire there would be no vapor from the diesel, which means there would be nothing to ignite.

If you were unfortunate enough to put gasoline in a diesel engine, you could cause even worse damage. Although the diesel gasoline mixture won't ignite in the engine, the unburnt fuel will make its way into the hot exhaust system, where it could potentially ignite and cause serious damage.

If you were to insert a very small amount of diesel fuel, then caught your mistake and filled up with normal gasoline, you might not notice much difference because the gas would be the predominant fuel. But if you do fill a whole tank with the wrong fuel, do not attempt to move the car. Call a recovery or breakdown service and have the vehicle towed for service. A mechanic will need to drain the fuel tank, clean out the fuel lines, and then refill the tank, which could cost several hundred dollars.

The good news is that this mistake is now very difficult to make. For one, diesel and normal gasoline smell and feel very different. Diesel fuel is very oily and much heavier. Diesel fuel doesn't evaporate in the same way that gasoline does, so it shouldn't smell as strong and you shouldn't be as aware of the vapor at the pump. Plus, cars that were manufactured in the last two decades have a plate under the gas cap preventing anything but the normal gasoline nozzle from fitting into the tank. The nozzle on diesel pumps is normally much bigger and would not fit into the tank of most modern cars. For trucks, motorcycles, and older cars, however, there's still a risk.

Refueling your car is an important job, one not to be done in a hurry or when you're distracted. Mistakes are always made, but when you're handling an expensive, flammable fluid, make sure you're aware of what you're doing at all times.