Petrol in diesel

[underfoot]

What happens if a small amount of petrol gets in a diesel engine

[New Forester]

When I made this mistake, the AA chap told me that up to about 10% petrol was OK in the diesel. I'd got the cans muddled, and when I ran out I put a gallon of petrol in. After being towed to a fuel station & filling up with another 9 gallons, it ran fine. I also realised why the outboard had been running so roughly...! Not sure about the diesel in petrol fuel, but I once saw a petrol Land Rover engine "not run" on half and half. Lots of smoke too... I worked out that the outboard had been running, just about, on about 1/3 diesel, but of course that's a two-stroke which has oil in the fuel anyway. I've also found in a laid-up car that the petrol in the tank eventually evaporates, leaving heavier oils (roughly like paraffin I guess). It was a devil to start, but just about ran when hot.

[alinton]

Nothing much will happen. The the petrol will still explode under pressure like the diesel, so the car will run. The explosions will be a little stronger and longer however so the engine won't run very well, and damage could be caused to valve seats and seals if done over a long period. Also the petrol doesn't provide lubrication like diesal does, so more damage could result over a long period. But mixing a small amount of petrol with the diesal won't do any harm. I accidentally put half a tank of petrol in a Land Rover Discovery once; I just filled up the other half with diesel and it ran fine. But diesel in a petrol car - BAD MOVE!