128i fuel tank size; only 24.2 mpg on highway

[orlandez]

Fuel tank size is listed in the manual as 14 gallons however even if i almost empty it (computer shows 10-12 miles left) i still cannot get more than 12.8 gallons when refuel. i tried different gas station but result is the same. i doubt that my tank size is smaller than spec but maybe computer setting is off so it shows lower fuel level. anybody experienced similar problem?

also i can only do 24.5 mpg on highway commute (about 50 miles each trip) which is way below 28 mpg spec. car only has 1400 miles on it so i hope mileage will be better once the engine is broken in. my previous 325Ci was averaging 27-28 mpg on the same route. any comments?

[Tomfrommd]

From what I can tell with my MT 128i convertible, the OBC miles to empty reading is assuming a one gallon reserve, even though the fuel warning light comes on with about 2 gallons left - BMW's published "reserve". In other words, when the OBC hits zero, you should have about a gallon left and the readings should start going -1, -2, etc. (This is even more annoying on some BMW motorcycles where folks run them down to MTE = 0 and then are only able to pump less than 6 gallons into the 7.1 gallon tank.)

With almost 3,000 miles, my highway mileage is now running about 28~30. I couldn't measure it for the break-in period as I tried to avoid steady speeds - but my overall average for the first 1,400 miles was 24.5 mpg. This included a lot of back road driving and not much city traffic.

Also have you checked your odometer and OBC MPG readout for accuracy? On previous BMW's, I've seen OBC errors of 6~9%, but my 128i is accurate within 1%. But for some odd reason, my odometer reads nearly 2% low, giving me slightly better gas mileage than indicated!
Tom

[Unregistered]

I've been able to pump 13.272 into my tank. but that is the most. obc indicated "--" at this point.