Gas Mileage Oddness?

This week I ran well over my normal mileage-per-tank. Didn't really think about it until the warning light came on and I filled up this afternoon. Entered it all into Fuelly and my mileage jumped 3.9 MPG from an average of 17.3 to 21.2 for this tank! Same mix of city/freeway/highway driving as usual.

Has anyone else seen a jump in their mileage like this? If so, do you have any idea what caused it?

 

i'd wait and see what ur next fill up says, this time, how many gallons did you put in? i've seen some gas stations cut off earlier than others, so maybe the one previously filled u more than normal, and this one cut you off more than normal? maybe the winter blend is disappearing?

 

should use the same pump at the same time of day for best results over a long period. differing temps, pumps, headwinds, tailwinds, crosswinds, traffic, etc. will play havoc on the tank to tank numbers from what i have found.

 

Too many variables to assign much significance to one tank filling. Like nammer said auto shutoffs on the nozzle vary in sensitivity, nozzle position can affect the amount of fullness attained. Keep track of mileage over a long time and look for trends.

 

Fresh vs old gas? Have found that if I fill up with fresh fuel after the tanks have been re-filled that I get better mileage. I guess it is because there is less condensation in the tank.

 

To add to the above posts, different stations/pumps can also be affected by how level the driveway is at the pump in addition to pump pressure affecting shutoff. Most of the time I can add 2.5 gallons after the pump first shuts off (but I always burn at least a gallon immediately and have had no problem with the carbon canister). ScanGauge gallons used to pump gallons to fill stays very close. On a road trip this gives me about 50 miles of "insurance".