fill ups

You are right, of course, that this issue will NOT effect mileage. The Prius doesn't take gas very quickly, probably because back pressure causes some overly sensitive pumps to shut down prematurely. The BP station where I regularly fill my Prius works perfectly every time but I once stopped at a station where I couldn't gas up at all from one pump. I gave up, switched to the next pump (wasting some money on higher octane) and it filled normally.

My gauge works as well as the one in my Explorer. With the Explorer, the reading varies considerably depending on how level the car is. It read low when parked nose down and high when parked nose up. For the most part, I ignore the gauges in both cars until they indicate 1/4 full. At that point I fill the Explorer knowing my range will be quite short. With the Prius, I start thinking about filling it over the next couple of days. :-)

Someone put me onto the 'rule of 10's' and I found this to work very well. Don't reset your mpg reading between fills. Multiply the mpg reading by 10 and fill when the miles on that tank approaches the product of that multiplication. So, then, if you are averaging 48 mpg on a given tank, gas up at or a little before you have driven 480 miles on that tank. My best tank so far ran 55 mpg and I gassed up right at 550 miles with a gallon and a half to spare.

I'm only running 48 on my current tank because I've had several short trips. I only get 35 mpg for the first 5 minutes after starting the car so a series of short trips can dramatically reduce fuel economy. FWIW, the same is true for my Explorer.

The Prius also has an "inflatable" tank - which I think causes the gas gauge to change non-uniformly across the tank.

For me, on the first 2200 miles I've noticed that I can go about 300+ miles on the first "half" of the gas gauge, and then about another 150 on the last "half".

This is annoying, and the gas gauge blinks when I have only used about