Underground temperatures have far less variation than the air around you, so it's very possible it's warmer than the air.
As for your fill up(s). Are you going to the same servo everytime? Stopping on the same click of the pump? Small differences like angle of the vehicle, when the pump cuts off etc can all factor into this. That and the reading the car has never been 100% accurate for me, more a close indicator. If all those factors align, that sort of difference is possible.
All of that said, fuel consumption is a long game, sign up to Fuelly and keep a running log, maybe next time it reads under! I wouldn't be blaming the servo over a single odd reading.
Fuelly - Track and Compare your MPG
If you're worried about a particular servo, go elsewhere and see if the problem goes away, maybe that one places pumps really aren't working right. It's possible, but if it continues else where it's probably you, after all there is always the other explanation. Your 15 - 20 year old sensors aren't quite right anymore.
Bookmarks