Help! I’ve put petrol in a diesel engine, what will happen to it?
What happens to your vehicle engine very much depends upon the amount of petrol that you’ve put in compared to the amount of diesel that may already be in the tank. Our wrong fuel engineers have come across all of the different scenarios involving petrol in a diesel engine, many times.
Very little or no diesel in the tank – If your vehicle has virtually no diesel in the tank and you inadvertently fill it up with petrol, when the engine is first started there will probably be enough residual diesel in the fuel system to get the engine going but the petrol will very quickly be drawn in from the tank and this will cause the engine to begin running roughly until it stalls altogether and won’t restart.
Half diesel, half petrol – Many motorists who fall foul of the petrol in a diesel engine mistake have stopped for a top up before a long journey. If you have a mixture of petrol and diesel in your fuel tank and the ratio is about fifty/fifty then, depending upon the vehicle and the type of engine, it may well run for a long while. In all likelihood it will run roughly though, and if you drive the vehicle regularly then you will notice something amiss.
A few litres of petrol in with mostly diesel – This is potentially the worst petrol in a diesel engine scenario over the long term. If you’ve just topped up with a few litres of petrol and haven’t realised your mistake, then the vehicle engine will most probably start and run fine. It may be a little rough but unless you know the car very well indeed, you may not even notice. This means that the petrol sits in the vehicle fuel system diluting the diesel fuel lubrication and this can lead to serious damage to fuel system components.
Why is petrol in a diesel engine such a problem?
The problem is quite straight forward. Diesel fuel acts as a lubricant for the fuel system components in a diesel engine. Petrol is a solvent with no lubricating properties. If the diesel fuel lubrication properties are compromised, then, where there is metal to metal contact between components in the diesel engine fuel system, excess friction will cause the components to wear quickly. This can lead to a build up of very small metal particles (swarf) in the fuel and if enough of these get into the engine injectors, it can spell disaster for the engine. There is another issue with petrol in a diesel engine and this is the solvent characteristic of petrol. If petrol is allowed to run through the vehicle fuel system for any length of time, the internal seals may be damaged by the solvent effect. Again, this can lead to a build up of tiny rubber particles which will also affect the engine injectors if they get through the fuel system.
Will I need a new engine?
It’s highly unlikely that you will need a new engine, you may need the engine injectors cleaned or some of the fuel system components changed. In some rare cases you may need replacement engine injectors and, depending upon the make of the vehicle, this can be expensive.
What do I do if I’ve realised that I’ve put petrol in a diesel engine?
If you haven’t already, don’t start the engine. Also, on some vehicles, even locking or unlocking the doors can prime the fuel pump and draw in a little of the wrong fuel type. It can be an awful shock when it suddenly dawns on you that you’ve filled up with the wrong fuel. We know how stressful it can be when you’re in a hurry to get somewhere or if you’re stranded in an unfamiliar place or at night. This is why we operate within a widespread network of professional engineers. We can get an expert to you, fast and they’ll arrive with the equipment needed, depending upon your situation. If you’re still on the fuel station forecourt or broken down in the middle of a busy main road, our engineer will act fast to make sure that you and your vehicle are safe. Petrol in a diesel engine is very unlikely to be a really serious problem as long as you get the wrong fuel type removed as soon as you can by one of our professional engineers.