Is there any way to see the instantaneous mpg on the gs400 without the nav system? Only way I can find is by recording miles per entire tank, and that takes time. Anyone know of a feature or faster way to do this? thanks.

 

even with the nav it wasnt very accurate for me the best way is the entire tank method or filling exact amount and measuring exactly when light turned on etc...

 

There isnt any 100% accurate method of calculating mpg because of all the variables that happen during driving. People blame on board mpg readers, but dont realize that it changes because of the driving conditions. As said above you can fill your tank till the nozzle stops you and drive around a few days, fill up again til nozzle stops and do a little math, however if the next day you'll have a different mpg for something simple as traffic that you may have not had the day before. The only mpg that is close to accurate is on the high way cause you're not doing stop and go driving, its just set the cruise control and thats it...

 

You are correct.

AND... even on teh highway, you cannot comapre to another members car due to difference in tires, tire life, wind, and alignment factors.

 

You could buy yourself a Scangauge computer. Plugs into the OBDII port.