Expansion of Petrol: Petrol expands when it is heated, and the expansion can cause the tank to bulge or even rupture if it is completely full. This is especially important in hot weather, when the temperature inside a car can rise significantly.
Vapour Lock: When petrol is too full, it can create a vapour lock, which is a blockage of the fuel line caused by the vaporization of petrol. Vapour lock can cause the engine to stall or run poorly.
Overflow: If the tank is too full, petrol can slosh around and overflow when the car is in motion. This can be dangerous, as petrol is flammable and could ignite if it comes into contact with a spark or flame.
Damage to Fuel System: Overfilling the fuel tank can also damage the fuel system components such as the fuel pump and fuel injector, which can be costly to repair or replace.
For these reasons, it is important to never fill a petrol tank to the very top. It is best to leave a small air gap at the top of the tank to allow for expansion and to avoid the risks associated with overfilling.
