“Full tank,” said a driver to the petrol station attendant. With that done, the attendant gave the ‘thumbs up’ sign and the driver smiled as he drove off the highly laden SUV, the sight of folded tents and bikes on the roof rack and a spade attached vertically along the rear door clearly attesting why he needed all that fuel: it seemed that a serious expedition was in prospect. “Great,” I thought. Maybe he was going bungee jumping. Why couldn’t I afford bungee jumping?
Anyway, as I sat in my battered Volkswagen sneezing in the Discovery’s choking wake I happened to reckon at the number of times I had done the same. (Not in my car of course, for if you fill my car tank fully it will then start leaking.) How about you – how many times have you filled your tank fully or been next to someone doing that? Well, here is the reason why you should avoid doing so unless it’s totally unavoidable. The mechanism that works the fuel pump is such that are two pipes inside the fuel dispenser, one of course to conduct the petrol into the hose leading the fuel into your car’s tank and the other to conduct it – away. This second pipe opening gets activated when fuel reaches the brim of your car’s tank, upon which a return-valve which is at the top compartment of the petrol dispenser is opened to allow excess fuel back into the storage tank. So what is the problem with such a safety measure?
The issue here is that while the pump meter counts forward, there is no allocation for it to take into account the fuel that has flowed back, and so you pay for extra fuel that you haven’t used. Another minor reason is that when you fill your tank fully, you do not provide space for the gas generated by the fuel in the tank and so up to a certain level (about three-quarters of the tank) when there will be enough space for this gas, more than necessary fuel will be sent into the engine for combustion. This fuel, though little, is mere waste as the engine will just burn what it normally uses in its combustion ratio.
Other than that, it’s totally safe to fill up because there are people who have raised concerns as to the expansion of petrol especially in high temperature areas, claiming that a car can explode when filled fully such that the petrol has no room to expand. Conversely, just as structural engineers take into account the movement of suspension bridges that will come as a result of the forces of wind and thereby make them flexible, so have automotive engineers built an air gap inside the petrol tanks to address the chemical volatility of petrol, and so your car is not at risk of exploding when the petrol expands in the tank. But if you are sensitive as to where every single cent of your hard-earned money goes, the best option for you is to fill up to three-quarters full.
In my case here, owing to certain financial and mechanical dysfunctions as already explained, I pump my ramshackle Beetle’s tank to a quarter-full and drive off listening to my favorite Beatles song, and as I join the main road I take one last look at the filling station and smile. The attendant sees that and smiles back – but he doesn’t really know why I’m smiling. Or does he?