The onboard computer in my 2003 MCS seems to think I'm getting 24.5 mpg.

Over that same time period, I have only observed 21 mpg (calculated when I fill up using the trip odometer reading).

I have noticed this discrepancy is consistent: the computer shows better mileage than I observe.

Does anyone know how the Mini's computer calculates the mpg?

 

I believe it guesses the fuel delivery based on the input sent to the injectors by the ECU, etc.

 

Inaccurately

The OBC in my 2002 MCS has always been over-optimistic.

 

Mine averages 11% optimistic, ranging from 1% to 19%.
I seem to recall some factoid that the car doesn't register the intake of fuel until a gallon has been put in. That would support the 11% delta, given I usually fill up near empty. But it still sounds weird. More likely that optimistic mileage is good for marketing.

 

My R56's OBC shows a consistent 30.3..............real life? 27.5.

 

It would seem my experience is not uncommon. Which leads to my second question, is 21 mpg low for a car with relatively few mods in normal mixed driving?

My 2003 MCS has a 17% pulley and a widened airbox, but no other performance modifications. About half of my driving is on the freeway, and I admit I have a hard time keeping my foot out of it. Still doesn't, 21 mpg seem a bit low?

 

Knowing the speed you average per tank would be more meaningful than describing the type of driving you do

I've gotten anywhere from 17 MPG (averaging 15.5 MPH) up to mid-30's (at freeway speeds) in my 2002 MCS with JCW Kit.

 

Yup...
+1
I know before my car was tuned, the odb was usually about 2 mpg off...then was more off when I added the jcw 380 injectors...
But when I was tuned...asked for it to be fixed...
And now, the obc is usually within a HALF of a mpg of when I calculate it at the pump...
I can get 29-31 mpg with a 45mph full tank average....usually running 70 mph with cruise, and about 30% stop and go...that is with 93 octane...the typical premium in my area...I do run (for winter 185 width 15" tires...#same diameter as the stock s 195/55r16)...and even my 16's are LIGHT (for OEM) rims...make a HUGE IMPACT compared to 17 s-lites, aka s heavies...
Remember, if you PUSH AND HOLD the obc button, you will reset THAT function...so you can average you fuel mpg or mph over multiple tanks or just one or less...

 

I just checked the OBC for my average speed, and it shows 6.8 mph. This is obviously a false reading.

I gather the computer must be logging the considerable time I spend in my driveway listening to radio stories with the engine off.

When I have glanced at the average speed in the past, it has generally shown about 45 mph. I feel like I should be getting better mileage with that average speed.

 

Also, I've reset the car's mpg tracker function multiple times, and it seems that over long periods of time - and numerous tanks of gas - it always seems to settle back to 24.5 mpg. So that's what the OBC thinks I'm getting (though it's clearly overestimating).

 

Yeah, 21mpg is pretty low for a nearly stock r53. You might want to start checking on things. Mine used to average 25mpg with mostly freeway and beating it like a rental in between.

Post mods, my obc reads 20% high. Says 25mpg when in reality I'm getting 20mpg with an average of 30mph.

 

At ~40MPH average I get ~29 actual MPG. At 60MPH it's 32-33.

 

I have a mostly stock 2003 r53 with JCW kit (basically just a pulley for 2003). My car shows about 24.5 mpg too compared to around 22.5 mpg actual. My average speed usually shows around 30mph.

 

Let you in on a secret....all OBC MPGs were programmed to lie.

 

Mine used to be accurate before I put injectors in.

 

Mine is consistently 4-5.5% more than manual calculation. The speedometer works the same way.

A German colleague once told me, "We Germans are innately a pessimistic people... except when we design MPG and speedometer gauges."

 

If you do a search, key word MPG, you'll find near 500 threads. This is plowing very old ground. Sales slip vs. OBC mileage calculations will never tally. Condition of injectors, plugs, pilot throttle management and time spent at stop lights are just too many variables to consider. The best thing to do is just enjoy motoring in a MINI. People ask me about mileage and my standard response is: "I don't know and I don't care." If I had a baby blue Prius then they'd know for sure.

 

Incidentally, I do have a Prius to offset my guilty pleasure from driving the Mini. My Prius MPG gauge is not dead on but is more accurate than the MINI's. Considering the Prius has all the variables mentioned and more so with the Hybrid Drive (battery charge/condition/age), you would think accuracy would be more difficult to attain.

 

For a daily driver to the office complex and back to the burbs a Prius is just the thing. We've go a hunk of Detroit iron parked next to the MINI for that kind of behavior. But, for 'motoring' the MINI has no substitute for enjoying the open road...except for maybe my long gone '62 XKE roadster.

 

My mini's display shows exactly the same (21.8 mpg) as my manual calculations.
Having said that, I think that it consumes much more than it should have.

 

Travis -

some modern V6 can get mid 20 MPG when driven normally. The size of the Mini is really there to fool us.

 

I've found most BMW OBC MPG readings to be 5-10% optimistic. Having been a long distance commuter on occasion one of the few things you can do to relieve the daily boredom is attempting to reduce ones fuel usage. With the R50, keeping to the 60mph sweet spot and driving with great anticipation and smoothness I have been able to get the OBC to show 43mpg at fill up, but then been disappointed when filling up brim to brim to have actually only returned 36mpg.

It seems to give you placebo pat on the back for trying to save the planet, but doesn't show pessimistic returns if you wring its neck.

 

mine is usually within .7 mpg of calculated, right now, im getting around 23-24, no freeway, and near full warm ups I atleaste let the coolant get to 100 deg before setting off

 

Would it be fair to say the given one vehicle and X number drivers and a near identical route, each driver would derive a different MPG result than the others just based on driving style?

 

Try resetting the computer? I avg about +/- 1mpg difference from computer which I think is plenty acceptable. I reset every time I fill up. Otherwise you're averaging over the entire car's life which includes winter gas and summer gas as well as different temperature ranges... all which effect your millage.

P.S. Mine says between 25 and 26 typically... which is 75% spirited, 25% hwy driving with a few mods. Get close to 30 on trips