Putting diesel in a gas car can make the engine stall and damage it. Don’t start the engine and have the tank drained.
What happens
Diesel is an oily fuel that doesn’t ignite properly in a gasoline engine. The engine may run rough, stall, smoke or fail to start.
What to do
- If you realize before starting, don’t start the engine or turn the key. Put the car in neutral, push it away from the pump and call a tow.
- If you drove, pull over safely and turn the engine off.
Fix
A mechanic drains the fuel tank, flushes lines and replaces the fuel filter. It costs about $200 to $700 or more.
Damage
Driving a long distance can damage injectors, the fuel pump and the catalytic converter.
Opposite
Gasoline in a diesel engine is worse for the injection pump.
Prevention
Diesel pump nozzles are larger and often green, so they don’t fit unleaded cars.
What happens
Diesel is a heavier, oilier fuel than gasoline. A gasoline engine uses spark plugs to ignite a fuel-air mixture, but diesel does not ignite from sparks well. It is a lubricant-like fuel that does not vaporize easily. If a small amount of diesel is mixed with gasoline, the car may run roughly, smoke, knock, lose power or stall. If the tank is mostly diesel, the engine will probably not start or will sputter and stall within a few miles.
What to do
- Do not start the engine if you realize the mistake before driving. Do not even turn the key to the on position, as that can prime the fuel pump and circulate diesel. Push the car away from the pump if possible.
- If you already drove and the engine stalled, pull over safely and turn it off.
- Call a tow truck. Do not drive any farther.
- Tell the service shop what fuel went in and how much.
Fix
The fix is to drain the fuel tank, flush the fuel lines and replace the fuel filter if contaminated. A tow costs $75 to $200, and draining and flushing costs about $200 to $600 depending on the vehicle. If you stopped quickly, the damage may be limited. Some shops can run a small amount of diesel through without damage, for example if less than 5% of the tank is diesel mixed with gasoline, but get professional advice.
Damage
Running a car on diesel can clog fuel injectors, damage the fuel pump, foul spark plugs, harm the catalytic converter and damage the oxygen sensors. Repairs for serious damage can exceed $1,000 to $5,000 or more. Insurance may cover misfueling in some policies, so check coverage.
Opposite
Putting gasoline in a diesel car is generally more dangerous for the engine. Diesel pumps and injectors rely on diesel as a lubricant, and gasoline can destroy them quickly. Modern diesel engines can be damaged by even a few liters of gasoline. Never start the engine if misfueled.
Prevention
- Check the pump label before filling. Diesel pump handles are often green in the US, though colors are not standardized everywhere.
- In the US, diesel nozzles are wider than the filler neck of unleaded gasoline cars, so a gasoline car usually cannot take diesel by mistake. It happens mostly in rental cars, with older vehicles or in countries with different nozzle rules.
- Slow down and pay attention at the pump, especially in rental cars and unfamiliar vehicles.
Fuel chemistry and repair costs
Diesel is oil based and heavier than gasoline, and it does not ignite properly in a spark ignition engine. A gasoline engine that gets diesel can sputter, produce thick smoke, stall and possibly damage the fuel pump or injectors if driven. Do not start the engine if you realize the mistake at the pump. Putting it in neutral and pushing the car away and calling a tow truck is best. The fuel tank must be drained and flushed, which typically costs around 200 to 500 USD at a shop, and filters and lines may also need cleaning. If the engine ran, damage can reach several thousand dollars. A small amount of diesel, under 5 percent, may be diluted in a full tank, but follow the advice of a mechanic. Putting gasoline in a diesel car is generally worse, because gasoline lacks lubrication and can ruin the high pressure pump. Diesel pump handles are usually green and larger, and the nozzle is too big for most gasoline filler necks.
Based on data from AAA and the US Department of Energy
