Large MPG Calculation Discrepancy

On average you should expect the computer to be about 2mpg higher than actual.
Apparently this is your 2nd fill-up not your first. If you didn't do the initial fill then the numbers mean nothing.

In any case the only numbers that mean anything are averaged over multiple tanks.

 

That's a 27% discrepancy. Did you top it up at purchase, or is it the case that the seller said they would deliver it with a "full tank"? If the latter, likely it was a bit short of full, comparing to your fill-up technique. Next fill-up will tell.

 

Maybe recopy the code for fuelly icon? Strange indeed that it's different.

 

FWIW our car computer seems to calculate the average MPG a bit high. 2-3 MPG higher than the manually calculated value I figure on fill ups.

 

If anyone reset the Trip & MPG display anytime later than the actual fillup time, erasing some trip miles for that tank, then your first fillup calculation will be bogus. It doesn't matter that the fuel gauge on the dashboard appeared full, 1-2 gallons could still have been missing.

[I don't have signature messages displayed, so can't see your Fuelly record.]

 

I settled on using the odometer readings, early on; no chance of accidental reset.

 

That doesn't help in this situation, when the filling in question happened before he acquired the car.

Absent these meter resets synchronized with refueling, the car's displayed MPG is also meaningless for comparison to hand calculated MPGs.

 

Relax. Focus on the results you get on the next few tank fill-ups. Look at those individual results. Your current results are probably skewed by events that occurred before you bought the car.

My '12 v MPG varies greatly with low MPG fill ups following super high ones or sometimes the reverse. But over time, the average varies very little even though individual tanks can include only in-town, up to the mountains, off to the beach, mixed driving, just me or 5 people and stuff for us for a week. And pump shut-offs vary wildly as does the quickness of my hand at reacting to the click of the pump. Fast and I put in less gas and my MPG is high. Slow and I put in more and MPG is low. My last tank was 1.4 MPG better than my 42.0 MPG long term average and that variation didn't affect my long term average one bit because there were so many that built that average. The 42 average has included 17 and 72 MPG fill-ups, both highly suspect. The fuelly average tells the truth over time.

And obviously driving style (I use ECO and Auto HVAV and just drive it normally. I'm not slow off stop lights nor do I slow others down.), tires (size and type), weather, terrain, etc all matter a bit.