Tank half empty or half full? Fuel pumps don’t care
Dear Car Talk: I know how much you love old wives’ tales, so I’ve got one for you.
My dad used to tell me that to take stress off the fuel pump and prolong its life, I should keep the fuel tank over half full. His reasoning was the less fuel in the tank, the harder the pump works, therefore shortening its life.
As the years go by, and the more I think about this, the more I start to think it’s baloney. Any thoughts to straighten my dad out? — Tim
A: To be fair to all the perfectly accurate wives out there, this clearly qualifies as an old husbands’ tale, Tim. So, let’s call it what it is.
We can give your dad the benefit of the doubt here. When he was growing up, fuel pumps were mechanical — they were run by a lobe of the cam shaft. And they were housed near the carburetor, in the engine compartment.
They sucked fuel out of the tank. So, if the tank was full, some of the fuel got pushed up the line by gravity — which probably did make the job of the fuel pump a tiny bit easier.
But, for the past, oh, four decades or so, fuel pumps have been electric. They now sit at the very bottom of the fuel tank, and “push” the fuel up the line.
So, it really makes no difference to the pump how full the tank is.
I suppose a full tank of gas would help keep the pump cooler, which could, theoretically, extend its life a little bit, but I’m nitpicking here.
So, I’m going to declare you both right, Tim. While it didn’t make much difference, your dad was technically correct that a full tank reduced the work of the old mechanical fuel pump a smidge — maybe half a smidge.
And it’s also true that for the past fourplus decades — due to improvements in technology — that’s been largely baloney. So you can both pat yourselves on the back and apologize to your wives for dragging them into this.
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