remmib

I have a habit of writing down the actual mileage on the odometer everytime I fill up the gas. From that, I can always caclulate the gas mileage based on the actual distance traveled and the amount of gas used. At the same time, I also reset the all trip computer counters.

What I find is that the gas mileage calcuated by the computer (the "mpg since last reset counter" ) is consistently higher than my calcuation by 2-3 mpg. Whenever it reports 25.3mpg, the actual number from my calcuation is 23.1, and when it says 23.4, the actual number is 21, etc.

Is that my gas mileage computer being overly optimistic (some time it'll read 35mpg, yeah right) or all C class are like that? Any thoughts?

CitronC230K_03

no mine reads about 25mpg. ive had it as low as 17mpg. i never get 35 or anything like that.

nicedeboy

yup, I found the same thing. It read that I was going one MPH under what I was really going. Sound odd, doesn't it?

Saprissa

I was pretty **** for the first 3 - 6 months of writing down the gallons per fill up and the mileage covered during each fill-up, and it was maybe of a dozen times by no more than 1 or 2 mpg's. I was satisfied, and figured there was a fudge factor, like going down-hill will add mpg's if you let go of the gas, and taking it easy going up-hill. So I quit worrying about it. As far as average, the ballpark seems about the same from everyone raging from 17 to 27 mpg.


_________________
Carlos
Saprissa@aol.com

CitronC230K_03

i havent written down a thing as far as gas mileage goes. i do reset the trip computers though every time i fill up.

levelr123g

what does it matter, when the car is empty you have to put gas in it!

jrct9454

ALL of the cars I've owned with engine management computers and dashboard readouts have consistently recorded lower fuel consumption [higher mpg] than real-world calculations from actual miles divided by actual fuel put in the tank. ALL. This includes MB, BMW, Acura and others.

Part of this is that topping up at the pump always causes inconsistencies that will make the logbook look slightly more pessimistic; the less I put in after the pump shuts off, the closer I get to the computer's number. Still, this pattern is consistent enough over a long enough period of time that I'm ready to say it just seems to go with the territory.

I always record the manual calculation in my log, not the computer's. Over the very long haul, I'd say the difference is on the order of 1.0-1.2 mpg, with the computer always on the optimistic side.

CitronC230K_03

definately my kinda real world calculations! :p

SUNILP

you can adjust this factor in the DAS system at the dealer under "INSTRUMENT CLUSTER" settings. You can make the necessary changes to make the readings more accurate based on real world figures.

Guest0001

Agreed

amdeutsch

Thanx for the tip. I guess I'm in the minority once again. Because when I do my numbers, tax reasons - don't ask, the computer numbers are lower than real world.

remmib

Can you elaborate? What's the DAS system? Some diagnositic computer?
Do I have to ask the dealer to do that? How would they know which way to adjust?

tyro

Nice tatoo on your shoulder Nobel C320 :p

HITMAN

ive gotten as low as 13 mpg and as high as 31

wingless

My MPG computer has been right on. It has been off, at most by less than 1 MPG, usually by less than 0.4 MPG and frequenty 0.0 MPG.

At each fill I reset the computer, so the numbers recalculate to the next fill.

There are two sets of numbers. I use the MPG since last resetm not since last start.

FrankW

wingless

No, that's the fuel level gauge. It is important to maintain a non-zero level.

This topic is for the fuel rate consumption indicator.

HITMAN

Ok you bought the car, your going to put gas in the car to make the car run. Who the **** cares how many mpg you are getting because you are going to put gas in the car anyways!

wingless

remmib

Well, if the mgp calculation is incorrect, I wouldn't trust the range calculation either. Whenever the gas empty warning light goes on, the first thing I do is to check the range indicator to see how far I could still go. Granted these are all estimates, but wouldn't you want to have a more accurate estimate?

Other reasons to care about the mpg calculation is to compare across cars, we have mulitple cars in the family, and gas consumption could be a factor in deciding which car to take on long trips.

I also interested to know if different gasoline brands make a difference in gas mileage....etc.

They wouldn't put the on-board computer there if MB doesn't think it's somewhat useful to have these stats.