I have a Mini R56, 2008, but my guess is that this question would apply to most cars, not just particular MINIs.

While driving, I often look at the mileage indicator. When in gear and not touching the accelerator when going downhill or some such, it will often show 99mpg, with the obvious indication of consumption of petrol very low over to distance traveled (coasting). I could also put the car in neutral, and given idle petrol consumption, still achieve high distance over petrol consumption (rolling).

First question is, does leaving the car in gear when not touching the accelerator, use an equal amount of petrol as simply rolling? Is there a difference in fuel consumption between coasting and rolling?

Second question: Does the Mini fuel consumption indicator calculate only when in gear or when rolling as well? If I roll a lot, with the intention of increasing my mpg, is this reflected in my avg mpg calculation shown?

Thank you in advance!

 

My understanding (at least for a manual) is that when coasting in gear, the MINI will actually cut off the fuel to the motor. However, if you take it out of gear then it will provide enough fuel to keep it idling. Can't imagine the difference is very much.

Not sure how well this strategy will show up in the onboard computer's calculations (other than over time the avg mpg should increase). You would probably have to go through several tanks, using each method, to figure out any difference (and doing that is going to introduce a lot of other variables).

 

There are readers you can plug into the OBD2 port that will tell you, among other things, if you are in Decel Fuel Cut-Off.

If you are in DFCO, you will use zero fuel. However, you are still spinning the engine so you will slow down quicker than if you were in neutral. So when you are coasting to slow down, you want to do that in gear so you stay in DFCO. If you are coasting just to go some distance, and your intent is not specifically to slow down, do that in neutral. Or if your intent is to slow down very gradually.

I'm not brave enough to turn the MINI off while it is still moving. I was with my previous car, but that car was much simpler than the MINI. Still, that gives you the benefits of using zero fuel while getting a longer coast.

 

As others have said, the ECU is cutting fuel delivery to the engine when coasting in gear. Although the display says 99.9mpg, you are essentially getting infinite mpg.

 

OK, I understand the mpg portion -- thanks!

But does MINI's mileage calculator engage only when in gear or when rolling out of gear as well?

Another way I could phrase the question... Does the MINI factor in being idle when parked or not moving (red lights) and thereby decreasing mpg because it is sensing fuel used over distance traveled (fuel is being used but there is no travel in this case), or does it "pause" the calculations when idling for whatever reason. Or maybe does it perhaps stop calculating when you see the double "- - . -" ?

Thanks in advance.

 

I am sure it is doing a simple calculation based off fuel used and distance traveled.

This happens regardless of what your car is doing, aka moving or stationary.

 

There are two MPG readouts available. One of them is "instantaneous", while the other is "trip". The instantaneous one is the one that changes constantly depending on your throttle position and gear and so on. It will go to "-----" when you are below a certain speed, something like 4 MPH. The other shows the cumulative MPG since the reading was reset. It simply divides the number of miles traveled since the reset by the number of gallons used. So it does count time idling and so on.

 

If you slow down while in neitral you'll see the instantaneous mpg fall, it calculate mpg while out of gear.

If you're stationary the average mpg will fall (shows up most just resetting it). That just calculates total fuel used divided by distance moved.

If you use a 3rd party ODB reader it may show you mpgs better than 99.9. We got that when coming down a mountain, I've got a picture of 257mpg for a trip milage.

 

Thanks all!