I know I have a mpg display (instant if you will). I also have a mpg display that I had always thought was a 'vechile use lifetime mpg' display as in from the day I purchased the car up to today xx.x is the total mpg this vechile has gotten. Is that wrong...instead is it really a 'from this tank of gas' display to the next (thinking not)?

My ride is a 07 hihy and the only reason I ask is that my mpg jumped from 26.9 to 30.3 and all of this ONLY due to an about 150 mile ride last night after going to the dealer (still deciding if I will fall back to a gas 08 highlander or not...sorry). The sales guy has an 06 and hihy and he was saying that if you keep it in the slash marks (above blue and below the 0? mark) then you can get good mpg (yes I know read the manual...buried some place in the house at the moment but cannot locate it). Anyway, so I leave the dealer without the 08 gas limited highlander (white pearl...love that color) and as I drive I start to play around with staying in the green zone (slash marks) and yes (lord forbid...driving slower). On the way home did that very much (even a few coast up the slight hills when possible), maybe driving 5 to 10 miles per hour under speed limit if/when ok to do so (it was late at night and little traffic).

So, if the 30.3 mpg listed on my mpg is true for the life of the vechile then what I don't under stand is, since it has about 7,000 miles on it, how only a 150 mile trip can push that average up so quickly? I mean 7,000 miles at 26.9 one would think means you have to drive a heck of a lot more miles at a higher mpg level before that 26.9 would move higher to any degree.

Thus I'm dumb...
someone please educate me on what I do not understand about this mpg display (sorry no nav on my system, just those two dislays (one in speedo and other above a/c).

Try not to slam me too much on the thought about maybe trading in the hyhi...have two cars presently rx8 rotary (yes it loves gas) and the hihy so was thinking of droppping down to one still. Also have a burgman exec scooter that gets about 50 mpg that I would like to drive to work (5 miles) so that would become my 'gas saving' ride.

After last night I may have to rethink my driving habits and if I want to let her go. Afer all 26.9 is nice but 30.3 is starting match the mpg of some of those small cars yet our 07 hihy is a larger/nicer ride. Do though like the bells the 08 model offers (power rear hatch, sunroof, a bit wider for the two font seats)....yes I know, 20mpg average most likely on a gas 08 but that is what my scooter would be for.