Is it better to fill up at the half way mark or to wait until empty?

[BBsGarage]

Originally Posted by anon9

The reason I'm asking is because everyone knows you get better gas mileage from a full tank to half a tank, but I've heard that doing that is bad because you're not cleaning out all the gunk in the bottom of your tank and in the long-term, you will have to get a new gas tank.

Never heard of this. I can see if it is an older car that has been sitting around for a while and the fuel tank has started rusting, but otherwise theres not much gunks to be had. Plus most modern tanks are some type of plastic.

Personally I fill up when I hit a 1/4 because I dont like going to the gas station any more often then I absolutely have to.

[dkjones96]

Originally Posted by anon9

The reason I'm asking is because everyone knows you get better gas mileage from a full tank to half a tank, but I've heard that doing that is bad because you're not cleaning out all the gunk in the bottom of your tank and in the long-term, you will have to get a new gas tank.

The fuel inlet is always at the bottom of the tank, the only 'gunk' to be had would be stuff floating on top and since gasoline is so thin not much floats on it.

[palemelanesian]

Originally Posted by anon9

The reason I'm asking is because everyone knows you get better gas mileage from a full tank to half a tank

That's only because the gauge is not linear. It doesn't mean you're getting better mileage. Almost all cars read above half for the majority of the time.

Here are my results from the last year. About 500 data points, logged from the Scangauge. My car has a little hiccup/stumble when it starts running low.
Attachment 1267

[theholycow]

Originally Posted by Robin Hood

bringing the fuel too low will wear out the fuel pump faster. Most pumps actually use the fuel in the tank to keep the pump cool and lubricated.

Agreed, The fuel pump in my GMC died prematurely at 140,000 miles due to my habit of running it down to fumes before filling. Since then I try to fill at 1/4 tank, leaving enough to cool the pump but not having to drag around the weight of a full tank all the time.

Originally Posted by PaleMelanesian

That's only because the gauge is not linear. It doesn't mean you're getting better mileage. Almost all cars read above half for the majority of the time.

That's so annoying. I've observed it on vehicles from many manufacturers. Any guesses why they do that? It's not like you'll notice on a test drive that you're down to half a tank and have gone 250 miles.