I just finished my first tank of gas on my new 2010 Cooper. I really took it easy on the pedal trying to coax everything I could out of the tank and was rewarded, as I pulled into the gas station with an average MPG for the tank of 41 MPG per the on-board computer display. Then the bad news. The actual MPG per the fill-up data was only 31MPG!

Does this make any sense? Can the computer be so inaccurate?

 

Did you reset the computer before or after you last filled up with gas? If it wasn't reading JUST that tank of gas, it would have reflected other driving MPG. They can be a little optimistic (1-2 mpg) but not 10.

 

I have given up on the OBC and only use my ScanGuage II for MPG. You can calibrate the SCII but the OBC seems to have a mind of its own.

The SCII is more useful for monitoring codes and actual temps on the car, but the MPG and trip data is fun also.

 

Ours is about 2mpg off....

But....

And the big but here is...

My Wife drives 114 miles per day to work and back. It shows up as 57 miles each way on Mapquest, Google, my Lancer and in the Lexus IS250.

In the MINI, it shows up as 106 miles per day....

So, after we factor that in, her usual tank average on the OBC is 38mpg. If you figure it out with the factory mileage, it says she gets about 33mpg. If you figure it out by correcting the extra mileage that disappears, she gets about 35-36mpg....The best tank we ever got, the OBC said 40.5mpg. It ended up being about 37mpg actual.

And this is with factory size wheels and tires. 16" X-Lites with 195/55/16 tires.

 

Hand calc is always the most accurate no matter what you drive. I do use the gallons used featured on my GM truck in the hand calc. It has proven to be accurate. That way no need to save reciepts and can check it over multiple fill-ups on a trip.

 

I just reread your post. If this was your first tank of gas (i.e. the dealer filled it up for you), you have no idea how full they filled it or how much it idled after they filled it.

 

Check the language setting on the speedometer menus. Lang must be set to US. If lang is set to UK then the system will use imperial gallons which are about a quart more then US gallons and you will read 8 to 10 mpg high.

 

I don't have time to look it up but the OBC is only estimating the mpg for the last 20 miles or so. I know when I was driving the downhill side of Vail pass in Colorado, the OBC was showing that I was getting 92 mpg and continued showing that for some time even when I started up hill again. As far as I know, the OBC isn't using actual miles traveled and gas used (they could do this if load cells were used on the fuel tank), but are using engine vacuum in some way to estimate the fuel consumption.

By the way, my fuel gauge isn't even close to the amount of fuel that is left in the tank. I know the mini's fuel tank is a convoluted shape and the load cells to weigh the amount of fuel could be a good solution - look at all the possibilities it could create when combined with the OBC!

I too share your disappointment in the OBC's fuel analysis and the array of gauges available to the driver. I hope they fix this on the 2011's.