IMO, I believe the vehicle gage. The manual needs ti be more than gallons in and reading the miles off the odometer. The gallons in is a big variable IMO. Personally I know that I can drive 5oo miles and vary how much goes in anywhere I want. The indivual hand nozzles cut off differently from one to another and the same one varies on day to day and how fast the fuesl is going in. Do you top off or over fill and not know it. I trust the onboad readout much more than manual calculations and it is usually close but read less than I get manually sometimes.

The you need gas is the mfg worrying about the **** lawyers again. Get what if you are half way to Calf crossing the desert and the next station is 127 miles away? that sort of thinking. It's ok to have it but I think we all do our own thing and buy gas when we want or need to.

The 4 Gallon of reserve when he computer tells you you are empty is a common complaint on all the Altimas from what I've read.

And I've never had a car with an accurate MPG calculation. I always do it by hand and the computer's almost always on the Optimistic side. Only 1 tank into the NAH and it was high by ~ 2mpg

I have read that you can make adjustments to how the computer reads vs real world with one of those scangauge II code readers.

I don't think the Scan reader will do that. I believe it takes the Exclusive to the Stealers Tool.

I'd like to believe the display gauge is the more accurate measure (it makes my mileage look much better ), but if the current pattern continues I can't. On any one tank, the hand-calculated MPG might be off significantly, but over the course several tanks those errors should average out. If they don't, then one of the measurements has a systematic error. And I think a 5% discrepancy in gas pump measurements would eventually get caught, so any error is more likely to be in the NAH instrumentation.

Well, some people say, it's difference in opinions that makes the world go around.

Exactly Sward, after 3-4 tanks the hand calculations don't lie...

Hand calculations don't lie as long as your odometer is accurate. I'm not 100% sure but I think they are also subject to about 95% accuracy factor. I believe that fanactics that are into road rallying have a seperate odometer that is calibrated to a much higher degree of accuracy.

It could be that people that are not getting what their electronic display is reading (either high or low) are off because their odometer isn't reading correctly - or it could be the computer that's off - or they're both off.

Wouldn't any error in the odometer readings affect both the hand-calculated and computer MPG the same way? I've been assuming that the computer is using the same raw data for both the odometer display and the MPG display.

As a follow up to my last post:

http://blogs.usatoday.com/ondeadline..._believe_.html

If it could happen to a Honda then why not a Nissan?

It could very well be that way - or not - I have no idea. Any Nissan engineers out there?

The only way to tell your true fuel mileage is to use one of those fifth wheels that Consumer Reports uses and a flow meter for the gas.