"An inch of time is worth an inch of gold, but it is hard to buy one inch of time with one inch of gold"
Which always says to me that its not worth it just use the quickest option
Take the example drcongo posted:
"Yesterday I had to drive to a nearby town, just 20 minutes away, and noticed that every single petrol station there was a good 5p per litre cheaper than my town. I might plug this into a map."
Assume he uses 30 litres a week (high end of average UK usage) that's £1.50 per week saving but assume the extra miles use half a litre, that takes about 65 p off the saving (ill not go into wear and tear) over 30 years of work 50 weeks a year this means a saving of £1,275 over 30 years ... sounds a lot but
20 mins away - this assumes 40 minutes per week over 50 weeks is 2000 minutes, and over 30 years 60000 minutes. Now assume you are awake for 16 hours a day this equates to 62.5 days of free time - more than two months of awake time
so as the saying goes... which would you prefer £1,275 saving or 62.5 days of time
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.
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.