Over inflated tires (like some of the folks here who are running 40 something lbs instead of the manufactures recommended 32 lbs) can mess with the speedometers calibration.

Yeah, and I'd be real concerned with safety. These are not high performance speed rated tires. Jacking up the pressure to over 40 psig and add the 100+ degree temps across the country does not fit well for 80 mph interstate driving.

Ok well I filled the tankf or the second time, I squeeze as much gas in the tank as it will take, until I feel it is close ot over flowing. Both times it appears the "Tank Average" seems to be from 1-1.5 MPG over what I manually calculated. I was hoping it woudl be a tad more accurate so I woudl nto have to manually calculate it, and I really don't like jamming all that extra gas in the tank.

"I squeeze as much gas in the tank as it will take"
Please don't. See http://www.epa.gov/donttopoff/ for why this is bad.

B. Goodman

interesting, thanks. Never thought any would get sucked back into the stations system, usually if I have ever overfilled int he past it has spilled over the filler neck, usually on older cars.

I'm not sure why everyone seems to give an extra squeeze or two after the pump stops. Your mileage reading should be no more or less accurate if you just stop fueling when the pump shuts off. Yes, different pumps may not shut off at the same time, but adding an extra squeeze or two will not make it any more consistant.

It's been documented that topping off your tank is not healthy for your car, and taking your average mileage over a number of tanks will smooth out any inaccuracies of different top-off levels. A half-gallon difference in fuel used will make a significant difference in your mileage over a single tank, but be relatively inconsequential over after 10 fill-ups.

I'm not sure why everyone seems to give an extra squeeze or two after the pump stops

I wouldn't necessarily need to anymore because after 21 fill ups I know how my tank reacts. However I started this because my company vehicle, an Explorer, can hold anywhere between 3 and 4.3 gallons AFTER it kicks off. Trying to calculate milage like that is impossible.

My Camry though seems consistant with where it kicks off. I simply have given it two squeezes (small actual amount of gas) to make sure it really meant to kick off as I have had times where the nozzel would kick off in my other cars because of pressure yet it took another gallon.

I believe I will start "slowing" the fill when it gets near the top and then stop when it kicks off. Perhaps not wasting the vapor can get me over the hump on my path to 39mpg

Perhaps it would also depend on the type of pump being used. Some might kick off earlier than others. Some allow for more topping-off... I suppose if one always goes to the same gas station, then there's going to be consistency.

"Some luck lies in not getting what you thought you wanted but getting what you have, which once you have got it you may be smart enough to see is what you would have wanted had you known."
-Garrison Keillor

I have done it that way with every one of my recent cars initially to see how accurate the MPG guage were. On my I30 and I35 the MPG reading was not reliable, consistently 2-4 MPG more generous than reality. My 04 TL and 06TL were pretty much dead on that after a few tanks I stopped manually calculating the MPG. So for the first few TCH tanks I wanted to make sure that I had a fairly consitent tank as with many of my cars I have seen the difference in when a pump clicks off can vary by 1-2 gallon difference. With the TCH going 10 tanks for me will probably be 4-5 months, unlike my TL where it would have been 8 weeks!