Wednesday, July 9, 2008

Fuel savings tips

I keep reading cute little ways to save money on gas. According to Slate, it's better to cool your car by opening your windows, rather than using the A/C, but only up to around 68mph. If you're going faster than that, the drag created by open windows is tougher on the engine than using the A/C, so shut the windows and crank it up.

Also, I read somewhere that a clean car is something like 5-10 percent more fuel efficient than a dirty one. That seems like a stretch, unless the dirty car is really, really dirty.

But here's one that's got me scratching my head. According to Discover, you should fill up your tank at night when it's cooler, since cooler gas is more dense and you pay for gas by volume. Is this actually true? What happens if you fill up your tank at night and then the next morning it's really hot -- your tank doesn't explode, right? Does the extra gas bleed off as vapor somehow? Can the gas cap handle extra pressure? It's been too many years since I took physics or chemistry. The equation pv=nrt seems appropriate here, but I don't know what to do with it.

1 comment:

Josh Putnam said...

NPR had a mythbuster segment at the end of May that dealt with a lot of these. The air/window thing seems to be a wash.

I love this dirty car/clean car one. Who tested this? I may actually be motivated enough now to go out and wash my car to perform a test of my own.