In short: bad things. Running out of fuel is bad news for your engine, whether you drive a petrol or diesel car.
Even before you get to the point of having zero fuel in your tank, damage can start to happen. The fuel at the very bottom of the tank could have sediment in it – something that usually occurs in older cars – which can damage the fuel lines, block the fuel filter and even damage the engine itself.
At the point of having zero fuel in your tank, your fuel pump will start to draw in air. This can result in the pump getting too hot, overheating, and eventually wearing out. And it gets worse for diesel engines too!
Running Out of Diesel
When a diesel engine draws in air instead of fuel, both the fuel pump and fuel injectors can become damaged. This is because diesel fuel is used to lubricate the moving parts these components have.
As well as this, when you run out of fuel in a diesel engine you might need to bleed the system to get rid of the air before you can top it up again with diesel, which is a job for a specialist.
Running Out of Petrol
If you have a petrol engine, running out of fuel isn’t great, but isn’t quite as bad as if you have a diesel engine.
When you run out of fuel, the engine will start to draw in more air. A petrol engine works by using a mixture of petrol and air anyway and is therefore ‘used’ to having some amount of air in it. This is why, in some cases, you can top up your tank with more petrol, and drive away as normal.
But that doesn’t mean to say running out of petrol is acceptable to do, you’re not going to do your engine any favours by running out of fuel, whether it’s a diesel or a petrol one.
What Should You Do If You Run Out of Fuel?
If you notice you’re running out of fuel, the best thing to do is to find somewhere to fill up before it gets problematic – it’s never safe to let your car run too low on fuel. If, however, you’ve got to the point of having next to nothing in the tank, you should:
1) Find a safe place to pull over – make sure your hazard lights are on.
2) Call for help – whether that’s a friend or relative that can help with getting more petrol to you, or roadside assistance if you have a diesel car.
3) Avoid pulling over on the hard shoulder of a motorway, it can be incredibly dangerous. Stopping on the hard shoulder should only be done in an emergency situation where you have no other choice.
4) Don’t put yourself in a dangerous situation.
One way to make sure you don’t get caught short is to carry a small amount of fuel with you in a jerry can for emergencies. The HSE sets out the various rules and regulations you must follow in order to comply with the law when carrying petrol, so be sure you check you’re carrying the correct volume, in the right container with the correct labelling.