I fly a 172P which seems to use fuel from the left faster than the right tank while selected to both.....or at least it did.
I used to have it filled to full in both tanks but now only go to full on the right and 3/4ish full on the left. The reasoning is simple, the vent is on the left tank and when the tank is filled (especially on a sunny day) the fuel pours straight out of the vent as it expands with heat, or as you taxi, hit bumps etc.
I regularly do a three hour round trip and the fuel burn on the outbound leg was higher than the return leg. Since changing my fuelling strategy it has balanced out.
Last edited by VP-F__; 3rd Jul 2015 at 13:15.
Reason: addition