[Dragon88]

How often does the average MPG reading update itself?

Since I reset it 500 miles ago, my reading hops from 37.6 to 38.1 and back, it has never shown any other reading, is this how it should be? Somehow I doubt its accuracy.

[IanS100]

I'm fairly sure that someone recently posted that it's the average of the last 10k miles (if you don't reset it), if so the readout will change every time the average mileage changes. How often it changes depends on how long since it was last reset & the way you drive/average mpg.

[xs2man]

I figure my MPG reading to be out by about 1.3-1.7 mpg. It reads too low.

I reset all the computers when I bought the car around 2000 miles ago. And reset the journey computer everytime I fill up.

My average on the main computer shows 36.6 pretty steady (i.e. it hasn't changed last 2 tanks), yet according to Fuelly, I am averaging 37.9 at the moment. So 1.3 mpg better.

Now, the journey computer appears to be slightly worse, with a slightly larger difference between calculated and shown consumptions.

Overall though, I am quite pleased. At least I know what its telling me is actually LESS than what I'm getting.

If you want to determine its accuracy, sign up to Fuelly.com and log your actual consumption and compare with the computer.

[swhoyle]

Originally Posted by Dragon88

How often does the average MPG reading update itself?

Since I reset it 500 miles ago, my reading hops from 37.6 to 38.1 and back, it has never shown any other reading, is this how it should be? Somehow I doubt its accuracy.

Mine is the same, It seems to have set readings, instead of creeping up, 51.1, 51.2, 51.3 etc it hops from 51.1 to 52.6 etc - It never shows a figure in-between

[Dragon88]

Yep, I would have thought it would gradually increase from 37.6 to 38.1 and vice versa, but apparently not! Perhaps it might have something to do with me only doing 12 miles each way to and from work?

That Fuelly.com app looks good, will give it a go thanks

[xs2man]

I forgot to mention also, that my fuel computer appear to increase / decrease by 0.3 mpg at a time also. It never goes by 0.1 mpg.

As an example, it will go from 36.3 to 36.6 mpg, but will never show 36.5.

[HighlandPete]

The reason for the non incremental changes is, we work in imperial measurements, the BMW OBC is working a conversion rate of 0.1 litre/100kms increments. (Try the math and find the figures we'll see displayed).

So nothing wrong with the OBC displays. Also it is an accumulated average and OBC accumulations used to go to something like 9,999 Kms, or miles. I believe the E9x models are the same.

The longer the period between resets, the less change we will see. Reset the mpg and drive different styles over a few miles, it will be changing quite a lot.

HighlandPete