I am now a bit over 1800 miles. Since a while, I suspect the onboard computer is not accurate and I discovered today that I am right.

Last week. I topped the fuel tank and I reset the counter. Today, I filled up again. Here are the results:

130 miles, 7 gallons........ about 18 mpg very conservative city driving.

Onboard computer reading: 26 mpg.

I have something going wrong here.

When some of you guys say 26-30 mpg city driving, you better do your own figures because it seems impossible.

 

The computer consistently overestimated by 2 mpg on both of my MINIs. A fillup of only 7 gallons can have quite a bit of error in it since filling a tank to the same level isn't all that easy. Keep records for a bit and then do the calculation on the totals. Your sample size is too small to declare a problem just yet.

I averaged 36.1 with my 2010 Cooper Hardtop over 21k miles and am averaging 32.7 in my 2014 Roadster S over 7k miles. Being retired, I rarely drive in stop and go traffic.

 

i average a min of 30 plus miles per gallon, r58s here, i have over 45k on the odo...i drive in a major urban environment...when i took a trip to the land of cheese ( wisconsin) set cruize to 63mph for the most part whilst on vacation...averaged 39mpg...that is via trip odo and gas fillups calulations...something is amiss if you are getting 18 mpg

 

This. If your particular gas nozzle had clicked off after eight gallons you'd be talking 16.2 mpg. The more times and the more fairly you calculate the more accurate your numbers will become.

 

As I said above, the figures are for city driving only and what bugs me the most is the discrepancy between what the unboard computer give (26mpg) as results and the real mileage and the quantity to fill up (18mpg). I don't believe it matters much if I drive 300 or 150 miles between fill ups.

Since I have unstable idle speed from time to time since the beginning, I am wondering if it is not related to a flooding problem instead of starving as I thought during the summer. I also noticed that the engine has a lot of clatter from the valve train like a diesel engine and the exhaust pipes are really dirty but there is no black smoke.

 

Did you reset the computer at your previous fillup or has it been calculating for 1800 miles?

It isn't the miles between fillups but the number of gallons you put in that matter for sensitivity of a one-time calculation. As previously alluded to, a difference of one gallon in the filler pipe from one fillup to the next induces a 14.9% error in your calculation if you're only adding 7 gallons. With 12+ gallon fillups the difference between calculated mileage and the computer ranged for 1.5 to 15.6% with an average of 5.5% over 21k miles for me. A single calculation isn't statistically reliable. Repeat it and then take it to the dealer if you still get a calculate 18mpg.

 

How often and how much time do you spend sitting stopped at intersections? You've got multiple random variables working against you and you need a longer time line. Manufacturers compile reams of data to come up with one number. One data point will not signal anything.

 

I have the JCW Coupe just like you. And mine gets about 26-27 MPG in town. My computer always says about 2 MPG better. I get about 31-32 MPG highway with AC. No way you should get 18 MPG, I don't care how you drive, how the nozzle shuts off, how much time you spend idling. Your gas mileage is way out of line for any Mini including my car which is the same as yours. From what you describe about the clatter like a diesel engine I think there's something wrong with the engine or the injectors, fuel delivery. A dealer should be able to diagnose the problem.

 

On the Highway only I average 39MPG, City only 27-28 and on my weekly traffic and highway commute 30MPG. Even on a run when on the car hard for hours worst I ever got was 23.

Something is wrong I would have it checked.

 

I am not the only one who reported excessive fuel consumption in the 18 mpg range and yesterday, I read it may be related to a faulty ECU.

It could make sense and also related to the other problems as noisy engine, idle stability and overheating.

You get 26-27 mpg after how many miles? To get 32 on highway seems good.

For sure, the dealer will have to fix it

 

It is hard to believe....... even my 2012 Fiat at 12K doesn't do 39 mpg on the highway.....

You may drive at 50 mph all time.

 

Still getting low gas mileage in vegas ? Yea, you should be higher unless you are in sport mode all the time and lead footing it. I know in very hot climates the gas can take a dip ( also because the air conditioning is running all the time ). If you just putt around and are not aggressive. I would get that checked out at the dealership.

When you are on the highway ( level flat, no ac ) what does the instant MPG say ?

 

The only way to draw a somewhat accurate MPG comparison between cars is to also take into account the average MPH/speed for a tank of fuel. So, 25 mpg at an average speed of 20 mph is very different than 25 mpg at an average speed of 35 mph or 50 mph.

 

 

The car was purchased in April 2014. But the mileage in town (26-27) has been consistent the whole time. The average MPH is about 32mph, always in sport mode and certainly not trying to conserve gas. My daily commute to work and back is about 20 miles. I think you're correct in saying a trip to the dealer is indicated. The other person who asked about instantaneous MPG, that's another thing you can do: go a steady speed level road and see what that says.

 

What is the total mileage on your car to achieve these figures?

 

Overall, the onboard computer is not accurate for any of the data it provides.........only the dealer or a repair shop with the proper scan tools can know about the fuel trim and other sensors and they will never tell you what is the problem.

 

Log you fuel usage over a minimum of 5 fill ups, preferably 10 - the Mini fuel tank isn't huge and variations in fill nozzle senstivity could lead to considerable variation (certainly when talking about 20-25mpg average).

There are on line fuel calculators/logs such as Fuelly that make life a little easier provided you are happy to type in your gallons and miles.

Fuel quality may also have an effect.

My partners 2008 Justa is averaging aroung 48mpg - thats mixed use, but mainly reasonable length journeys of 30 miles, mixed with local city short trips. My commute is 30 miles, 26 miles of inunterrupted highway at 60mph, the remainder light city traffic - 50-53mpg on the OBC is typical, and fill ups suggest the computer is only a little optimistic. 95RON fuel in the UK though.

I think you have a couple of issues going on

- one is the supposed poor mpg (maybe 26mpg is typical for low ron fuel, hot climate and city use)
- the other the discrepancy with the computer which seems excessive.

 

Let's not overlook the fact that a US gallon is only 83% of an Imperial gallon. Fuel formulas in the US can also vary from state to state and season to season and often contain 10% Ethanol.

 

In my 2010 JCW Clubman, my first 2012 JCW Coupe and my Current 2012 JCW coupe I have gotten a solid 33 - 34 mpg around town. And I am not taking it easy. I rarely get above 45 on my commute, but I ramp up quickly.

 

Now, It is a very good point and it brings some reality and common sense. So, in America, I can believe somebody that says he can achieve 24-26 city and 32-34 highway and I will be happy if I reach these figures.

 

New jcw coupe here. I have had two fill ups so far averaging about 27mpg. Same as my old 07 Cooper S. Using 91oct California gas filled up at brand name stations. Chevron/76.

If you are getting 18 that is pretty low. It's hot enough here in the summer (consistent 80s/90s) my fuel usage with my old r56 never changed with temps.

I would see the dealer.

Also, are you using premium gas? I haven't read the entire thread perhaps you said that, but maybe that is a variable that hasn't been accounted for.

 

PREMIUM 91 all the time.........95% City driving. Summer here....110+.

For the next two weeks, I will be mostly on the freeway cruising at 80 mph and I will see.

 

Not a coupe but close enough...

I keep a very detailed records of the MINI stats and here is what I get and the car is always filled with 93 gas rating.

Total average calculated since we bought the car 26.4 mpg

Total average displayed since we bought the car 25.7 mpg (every time I get gas I write it down on the receipt. This is the average of all those times)

Best calculated on highway driving between around 65/80 on average 33.6 mpg at outside freezing temp, with heat and heated seat on.

Lowest mpg calculated 25.6 mpg in late spring probably during sunny days when over using the S button

So it's not the high mpg some who do more highway driving see but it's still within expected numbers I'm guessing. We just have a bad combo of stops, lights, and hills around our here.

 

The way I drive the gas mileage is way down. My wife had a 6-week job 50 miles away and drove the interstate about 60 mph and got about 40 mpg. Slower speeds will give better mileage. When we take a trip and I am driving I am busting 10 mph over the speed limit on the highway and getting 31-33 mpg.

My spedo is also off about 6 mph at 80 - the car shows 80 and my GPS shows 74. The odometer is about 30 miles further than actual miles run per the GPS per tank of gas. The GPS is accurate compared to my other vehicles (two have certified spedo's). It is more accurate at slower speeds but the computer mpg vs. actual is plus or minus 3 mpg for every tank. I am still on the original tires at 33K miles - they will probably last another 7-8k miles when they will get changed out to non-run flat tires. I will be going with a larger circumference tire to get the speedo more accurate. This is one of my few pet peeves with this car.