I imagine it's due to evaporation that happens overnight... Is it? And if so, would I save gas by filling it up more frequently? (Less room for the gas to evaporate into if I keep the tank more full)
Are your temperatures fluctuating? My guess is that it's due to the "bladder" in the gas tank expanding and contracting with the temperature changes. There shouldn't be any evaporation going on into the outside air as that is a violation of EPA regulations.
How about the air temp? Gas expands when warm and contracts when cold. Indy cars use liquid nitrogen (-325f) to cool their fuel before filling up for the race!
No Bladder in the 2011, as I understand it. Not talking about evap to the outside. Rather - within the closed feul tank, there will be liquid fuel in equilibrium with gaseous fuel. THe more empty space in the tank, the more gaseuos fuel, relatively. It is cooler in the morning. That could be it.
The Gen III Prius does not have a fuel bladder. The bladder was used only on the Gen II NA models. Modern fuel systems are sealed to prevent evaporative losses. The one on your Prius self tests at night; any leak would throw a code, causing a warning light on the dash. Fuel gauges in cars are not precision instruments, so don't expect precise readings. They are also damped, so you won't see quick variations. My guess is that your parking situation introduces some variation in the displayed level, but there isn't enough time for it to react when you pull in to park. Starting the next day you see the variation. Tom
