What damage could be done to a diesel engine if four liters of unleaded petrol was accidentally added to 40 liters of diesel?

Answer 1

Shouldn't cause any damage! Adding 10% of petrol to diesel fuel was standard practice in sub-zero winters in the days before "winter-grade" diesel. It helps prevent "waxing" where the diesel fuel will turn into something like a soft candle wax at low temperatures. You may notice a slight loss of power until the petrol is out of the system. 4 litres in 40 litres of diesel should not damage your engine, the one thing it will do is give you MORE power as it works a little like a bottle of injector cleaner that you may add to a tank of diesel from time to time. It will cause higher temperature explosions in your combustion chambers and a little more power.