My OBC is the same so far (1300ish miles). Will be low by 1mpg. But on a long 3 hr highway trip the OBC said 28.3 mpg but when I filled up and calculated it, it was 32mpg. Based on that you could be getting 25-26 which wouldn't be bad for all city driving.

MINI as well as BMW OBC's are notoriously wrong when calculating mpg. A former friend of mine has an escalade which I believe actually measures the fuel used, he complained about it being off by the second decimal place when he calculated it. HA!

 

I know I'm stating the obvious, but I hope every one who compares their calculated mileage with the OBC resets the onboard every time they fill the car and do a calculation. If you don't do this the result will be invalid unless you do both the OBC and the manual calculations over a long time period and then compare the average of both.

My opinion is that the OBC is probably more consistantly accurate than manual calculations, at least for most people.

 

Great, I'm moving back to Monterey from here in San Antonio, TX in July. Here I'm getting about 30.5 mpg in the city in my '05 MC manual. However, my wife's MCSa only gets about 21-24 mpg.

 

We must be laid-back in our driving as we average 32mpg with our 04 CVT.

 

And pray tell, how do you arrive at that conclusion (that the OBC is probably more consistantly [sic] accurate than manual calculations)? In my experience, miles driven divided by fuel used is pretty hard to question. Unless of course, the wrong values are entered....

 

You must be VERY laid-back if you are getting 32 mpg (in city driving????).... Are you relying on the on-board computer, or manual calculations? 32 mpg is almost at realistic hybrid gas consumption levels (and even a CVT MINI is more fun than a Prius).

 

I just got home from a run to Savannah to see #1 daughter. I averaged about 31 on the road, driving (usually 5 mph over, thought there we times I stopped myself at 90). In town I am about 28, mostly city but we do have bursts of 50-55 MPH.
I also started tracking my mileage on the web site below:
http://www.myautolog.com/default.asp
That's where I keep track of the mileage over time. I also NEVER relie on the computer to figure out the average since it was always 2 - 2.5 above actual.

I would think 21 is low but not driving an automatic am not sure. Just sounds low for a non S.

 

Every gas pump doesn't pump the exact same amount for a gallon of gas for one thing. Another thing is very few people fill their car up to the same point each time, (please, no gas on the paint). If you depend on the auto shut-off, that works a bit differently from pump to pump and depending on how far the nozzle is inserted. Even the time of day you fill up can effect the calculations. I hope there would not be any math errors, but that's not out of the question either. I don't know exactly what the OBC looks at, but since it isn't a human being, it can't make human errors, (like misspelled words).

Many who talk about the inaccuracy of the OBC either:

1. Didn't reset it when they fill up and are comparing an average mileage on the OBC to a one tank manual calculation.

2. Say it must be wrong because the, "miles left to empty", sometime goes up while you're driving. This would happen if you were, for example, driving in the city and then outside the city on an open road.

If over a long period of time you manually calculate your mileage and keep an overall average then, yes, that should be pretty accurate. I don't think most people do that. If you want to improve your mileage just drive in a matter that increases the OBC mileage figure, if your "real" mileage is 1 mpg more or less it doesn't matter, it's the consistency that counts, and that the OBC should have. It has no choice but to do the same thing every time. That may mean it's off a lot every time, but I don't think so.

Maybe I'd have less faith in the OBC if I knew exactly what it was looking at.

Do you know?

 

Fair enough regarding pump fill procedure. Personally (and I plead guilty to being obsessive-compulsive), when I am doing the calculated mpg fill procedure, I:

1. Refill from the same gas station,
2. Use the same pump,
3. Try to refill at the same time of day, and
4. Fill until the auto shut-off activates the first time (no topping off).

The above procedure tends to eliminate variability from the dispensing side. I also attempt to drive a route and re-trace it so as to eliminate variations from grade and wind direction.

Using the above approach has consistently yielded a calculated mpg result (miles driven divided by gallons of fuel used) that is 2-2.5 mpg better than the on-board computer provides (and yes, I do reset it with each fill).

Not really (know how the OBC does its thing). I presume the fuel guage is an input into the algorithm that calculates average fuel economy. If I am correct (about the fuel guage being an input into the algorithm that calculates average fuel economy), then based on all that has been posted about the variability of the fuel gauge display of fuel level, I would have serious doubts about the accuracy of the OBC's calculation of average fuel economy.