[BHarvey]

Originally Posted by HilseeJ

I actually don't run through a full tank. I do it by halves.

The method I use:
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Fill up tank.
Reset trip meter. (if you don't have one then write down your mileage)
Drive around until half tank.
Fill up tank.
Divide miles traveled by gallons that you just pumped in tank.
This is your miles per gallon.
Repeat multiple times to compensate for different pumps and average.
===
My understanding is that the first half of the tank is the most efficient as well as easier on the fuel pump. However, I'm not that mechanically inclined so I'm merely going off of posts made on this forum.

Using the same method above only running through a full tank will still be accurate.

Also realize that this will waiver from pump to pump so getting an average is the ideal thing to do. Some pumps might give a little more fuel before stopping the flow, some a little less.

Obviously topping off will skew the results.



If the online calculator made the assumption that because you were at 3/4 of a tank on your gas gauge you burned 3/4 of 12.2 gallons, then no, it's not legitimate. Same applies if your gas needle was at half and the online calculator assumed that you burned half a tank.

I have traveled 115 miles and my needle was still on FULL 100%.

The method I listed at the beginning of this post is the only fool-proof method I am aware of to get an accurate mpg reading.

The problem with this method, is, say you have a 11 gallon tank.... and you have a +/-.25 gallon error
200/5=40mpg
200/5.25=38.1
200/4.75=42.1

VS.
400/10=40mpg
400/10.25=39mpg
400/9.75=41mpg

See the difference? Half the error when doing full tank.