When I drove my 2011 CMS all4 home from MN, I got a solid 30 MPG (automatic) during 9 hours of highway driving. Now, it seems the best I can do is 24-25 mpg averaging about 78 mph on highway trips. Is the 93 octane 10%Ethanol gas I'm buying here in MI different than the 93 I was buying in MN, WI, IL? Wondering if having it re-mapped is doing it. I can only get decent mileage while driving at 60 mph now. (above 27 mpg)

Could carbon buildup be an issue. I was going to try some Gumout, valve cleaner, fuel system cleaner , and/or Octane booster.

 

Not sure what is causing the reduced gas mileage, but I doubt it would be carbon buildup on a 2011 model due to the low miles on it. Have you checked the tire inflation per what they recommend on the door of the car? This is usually good for 10% reduction or improvement in MPG. Have you change the tire size, larger wider tires reduce MPG

 

78 mph average will not give good fuel economy. Aerodynamic drag increases with the square of speed.

 

Yeah, these li'l bricks aren't very slippery!

Dave

 

Tires are the same, as when I got it, and the only thing I can figure is once I found out via handheld GPS that the speedo reads 3 mph faster than actual, that I am pushing a bit more at higher speeds.

Slippery eh? Maybe a quick coat of Crisco on the hood will do the trick.

 

We have averaged 24.6 mpg no matter what fuel brand, octane rating, tire inflation, or city versus highway versus sport over standard. Aggressive or like grandma.

It doesn't matter the best mileage I have ever gotten was 25.1 in a tank. And that is calculated on mileage versus fuel purchased over the course of a two day 800 mile trip.

This car is severely over estimated in regards to fuel effiency.

 

Just confused as to how I could get 30 mpg on the trip home, then nowhere near that afterwards.

 

Maybe it was all downhill?

 

Tail wind.
I was getting about 30 driving it like I stole it and now I'm getting about 26. Not too bad but my beetle gets a legit 30 driven the same way. My clutch is slipping so maybe that would get better after replacement. I would think this little cart could get at least 35...

 

Haven't got less than 26 yet, avg 28-30 and a high of 36

 

I got a boost/vacuum gage and by watching that and keeping it in the vacuum range, I can get better than 30 mpg. But, if I keep my foot in it, I only get about 25 MPG.

Dave

 

I never have matched the mileage I got on my 2.5K trip returning home with my new MCS. I attribute it to two things: 1) I was taking it easy during break-in; and 2) it was 100% highway driving, with almost no stop-and-go for hours and hours with very few stops. Whenever I check "highway" mileage now, it usually includes at least some chunk of urban and/or cycles where I have parked the car overnight. These bring the average down.

And don't discount tailwinds. For any given trip, they can be a huge variable causing mileage to go up/down 20% or more.

I doubt anything is wrong. Your car is rated 23/30 and the EPA highway 30 assumes a lot slower speeds than 78 mph.

- Mark

 

We owned a 2005 mini cooper and averaged 32mpg in the same commute, driving conditions, driver, worse gas from discount station and less octane.

Now we are at 24.6 average never once higher than 25.1. Something is not right.

Overall I would say this car is not rated properly. Have a look at comparable vehicles that rate their mileage. most will be within a small percentage of the combined average. Like .5 to 2 percent.

The suggestion that the wind, hills, or other unavoidable factors is not an arguement that contains any weight in this discussion. We are talking about 14 months of driving in a variety of condions, speeds, parts of the country, fuel grades, manufaturers,etc, etc, etc..

This car falls short of expectations no matter how it's sliced.

 

Are you going by the car's mpg display or are you manually calculating your mileage? The car's mileage calculations are notoriously inaccurate. The only way to get an accurate mileage number is to calculate it yourself when you fill up.

Dave

 

I've found that our 2012 CMSA4 manual can easily beat our stock 2005 R53 MCS manual when driven the same way in mixed urban driving, even though the R53 is 600 lbs lighter. In fact it is easy to beat the EPA city rating of 25 mpg, while it required more concentration and restraint to get the EPA city rating with the R53. So I would say the EPA city figures are conservative for my type of city driving with this car.

I haven't done much highway driving since completing break-in, but I will do a longer trip this weekend and report results on Fuely.com. It's going to be warm so I will use AC set at 76-78F, my usual setting.

I use a Scanguage set to show boost and fuel flow rate and can confirm the post above about keeping the intake manifold pressure mostly in vacuum to get low consumption. For instance, when going up a steep hill near my house, running in 2nd with vacuum gives lower consumption than using 3rd with boost to maintain the same speed.

 

My first 7 fill-up data by hand calculation and vehicle computer:
hand computer
25.7 25.1
29.5 31.3
29.8 29.1
26.1 26.2
30.1 29.6
28.7 28.1
27.1 28.2
averages
28.1 28.2

My Scangauge tank MPG display is being calibrated each time I fill up, but it appears that on my car the computer MPG is rather accurate. My fill technique is to let the pump shut off automatically, then restart it and let it shut off once more.

 

It would appear your car is doing what it should.

The poor mileage of our car I believe is a symptom of the underlying issues this car has. Two thermostat housings, one fuel pump, a firmware upgrade, oil temp sender,front bake pads and sensors, etc. etc. ...

We are waiting for another part from Germany right now as well although it is unrelated to the drivetrain.

24.7 showing on the computer now. It never varies more than .5 +/_. Actual mileage computed by fillup devided by mileage accrued is consistant or slightly lower than the computer.

We get about 250 miles before the single illuminated fuel bar is up. 220 to 230 for the 2 bar.

This is over 14 months. It is at least very consistant if not very good!

 

Update on the mileage since the new high pressure fuel pump was installed.

Computer averaged us out at 23.2 mpg
Actual fuel computed vs. mileage ....

22.9

Yeah!

Combined city highway driving and I get just over 250 miles to the tank.

This car is a POS!

 

My last fill gave 29.2 mpg hand calculated, average speed 28.3 mph, approx. 75% urban.
The car computer displayed 27.4 mpg. First month with warmer weather is helping fuel economy I think.

Going to do our first highway trip in warm weather this weekend. I am also trying the high-speed setting (38 psi) for tires this time.

 

I took my first long(ish) road trip last Saturday, and was pleasantly surprised to get 32.5 MPG! That was doing a lot of up hill driving here in the CO mountains. I wasn't Driving Miss Daisy either!

My calculation was made by miles driven divided by gallons to fill.
Sport button was off.

 

still getting very consistently in the 25 range.

Fuelly shows every other tank at 24mpg or 26 mpg.

 

On this trip, 481 miles all highway with a few stops, we averaged 34.3 mpg as measured on a calibrated Scanguage. Cruise set at 65 mph (on GPS), moderate to gusty tail and side winds, temperatures 71-90F, AC set to 74F, elevation loss and gain 700'.

 

I have noticed the cruise control is very good at gentle throttle application.

On roads with moderate hills (no steep inclines) with the speed set to 62, my realtime mpg never dipped below 20.0.

on the flip side though it never reached 99.9 on the downhill slopes either.

 

were you using fuel with ethanol or without ethanol?

 

I used normal California spec gas with ethanol (Chevron). Actually on this route I could have stopped at Thunderhill Raceway near Willows and picked up some good high octane non-ethanol unleaded race gas. I'll try that some time!