Is ‘topping off’ when the gas pump stops by itself while fueling?
If you decide to fill up your fuel tank, the best shot is to stop once the fuel pump clicks off and stops by
itself. The fuel pumps mostly have sensors that make them click off once the fuel from the tank touches
the tip of the nozzle.
Topping off is when you keep clicking the handle to get a bit more and then a little more gas in the tank.
This is a problem with modern cars some decades back basically. These cars have vapor recovery
systems. These systems take the vapors off the top of the tank at the filler hose and keep them from
entering the atmosphere. It is a pollution reduction system. This system has a charcoal canister. It is
designed to deal with vapors, not liquids. If you keep clicking the gas pump handle to put a bit more and
a bit more gas in there, you risk filling the vapor recovery system with liquid gas. This can damage the
vapor recovery system, turn on your check engine light and cost you money.
Be aware, that sometimes those handles don’t click off by themselves every once in a while, so be on
standby as your car fills up and be sure the pump is stopped if necessary. Which implies that it works
this way only if both your vapour recovery system works and the fuel pump has that functionality
If the fuel nozzle clicks off before your tank is full and it happens often regardless of what station or
pump you are using, then there is something wrong with your tank’s evaporative emissions system and
you should check it out. Note that if you overfill the tank, it could spill on your car around the tank and
with time, the colour of the car in that area will be pretty messed up.