I've been wondering about this, too. It has been obvious to me that it starts with the previous reading (which is DUMB). But, the number has to be calculated from distance divided by fuel used. So, when it starts with the previous reading, what "distance" and/or time is it using as the basis for the calculation.
For example: If I'm parked when I reset it, then it should say 0 MPG until I start moving. (that's what all my Fords that I've had have done). Then, when I do start driving, whenever I've driven far enough to use 1 gallon of gas, it will show be showing the distance as my MPG.
The way the Dodge works, if I sit there and idle until I've burned 1 gallon of gas (obviously, I wouldn't really do that), it ought to read 0 the whole time. But what will it really read? If it starts off reading, say, 12, and I idled away 1 gallon, and it now read 6, that would tell me that it was starting the reading based on the previous 1 gallon usage. But, if it started as 12 (after a reset) and I idled away 1 gallon, and it now read 8, then I would know the reset set it to the MPG for the previous 2 gallons usage.
Like I said, the way it works seems dumb to me.
Last edited by StuartV; 01-12-2010 at 02:53 PM.