[oniony]

I've also wondered about whether to fully fill my tank or drive on a small amount so that I'm not using fuel to carry fuel. Do you know of any metrics on that?

[embedding-shape]

I haven't made any calculations, and it's more a hunch, but considering you usually need to remove hundreds of KG in order to make an impact on how much fuel is being spent, 40-50L of gas (~40KG difference between full and empty maybe?) would have an marginal effect on how much fuel is spent to carry a full tank vs 10% filled tank.

Besides, with a smaller tank, you'll make more trips to tank it, and also have less choice to go to gas stations that are further away but have cheaper price. Then again it becomes a question of "Do I want more time or more money?", back to square one :)

Edit: Also, someone correct me if I'm wrong, but doesn't the fuel pump use fuel itself as a coolant or something? Never investigated myself, but some car-knower once told me that running the tank on low always isn't good for the fuel pump, or something like that. If that's true, running with 10% of the fuel would mean more maintenance too, potentially removing any savings in the first place.

[jansper39]

> Never investigated myself, but some car-knower once told me that running the tank on low always isn't good for the fuel pump, or something like that.

The main issue is that it risks pulling detritus from the very bottom of the fuel tank, usually a bigger issue in diesels and I suspect less of a problem these days.

[alias_neo]

> doesn't the fuel pump use fuel itself as a coolant or something

I know very little about these things, but my understanding was always that any form of liquid pump uses the liquid itself as coolant to some extent.

[maffyoo]

you can probably work it out but you have to make a lot of assumptions :)

Ultimately how much is your time worth? in the example given drcongo's time is worth £1.28 an hour.

[fragmede]

Unless you're driving a lorry with a 120L tank, it's negligible. We're talking like, 100 mL per 100km.