What damage does the wrong fuel cause?
The damage — and the cost — depends almost entirely on one thing: whether the engine was started.
Petrol in a diesel
The most damaging misfuel. Petrol strips the lubrication the diesel high-pressure pump and injectors rely on; running it risks metal wear and debris through the whole fuel system.
Diesel in a petrol
Usually less severe — diesel won't ignite properly, so the car runs rough or won't start, but it rarely causes the same injector damage.
Damage questions
What happens if you put petrol in a diesel car?
Petrol acts as a solvent in a diesel system and reduces the fuel's lubrication, which can damage the high-pressure pump and injectors if the engine is run. If you haven't started the engine, damage is usually avoided — the fuel just needs draining and the system flushing.
What happens if you put diesel in a petrol car?
Diesel is thicker than petrol and won't ignite properly on the spark plugs, so the car typically misfires, smokes and stalls. It's generally less harmful than petrol-in-diesel, but the tank still needs draining and flushing before you drive.
Will petrol damage a diesel engine?
It can, if the engine is started and run, because petrol strips the lubrication the diesel pump and injectors rely on. Caught before starting, a drain and flush almost always prevents damage.
What damage does petrol in a diesel cause?
The main risk is to the high-pressure fuel pump and injectors from lack of lubrication, plus possible contamination of the fuel lines and filter. Severity depends on how much petrol went in and whether the engine was run.
Is red diesel bad for my car?
Red diesel is chemically similar to normal diesel but it's illegal to use on the road and the dye can flag up in checks. If it's gone into a road vehicle, it should be drained and the system flushed.