wotbill

Hi all,

I have an 2011 E350 Bluetec with about 650 miles on it and I noticed the instrument cluster indicated fuel economy since reset (I reset at fill up) was 32.3 mpg (roughly 60% highway, 40 % metro rural) but the calculated (actual miles/gallons) was only 28.0 mpg.

I'm shocked at the disparity since I was expecting the readout to be optimistic by 1-1.5 mpg but not over 4 mpg!

I used the same pump for fill ups and used the auto shut off. Even allowing for a 1 gallon (!) error in filling (auto shut off permitting an additional gallon) yields 29.8 mpg. Still over 2 mpg short of indicated....

Anyway, just soliciting feedback from others who may/may not have observed the same thing.

Thanks!

BudC

I kept track of the fuel I used on a 6,000 mile trip driving a 2008 E350. The computer was optimistic by 1 MPG.

The same car over a 10,000 mile period of all city driving showed an average of 18.7 MPG. I don't think it was off more than 1 MPG.

I think you have to check your mileage over a longer range/period since with that diesel, you haven't had many fill-ups.

cvinfig

I have 6000 miles on my Bluetec and see the same numbers as you: 32ish displayed / 29ish calculated.

ImInPA

Your assumption on the gallon variance is the only variable in your calculation. I have filled my Bluetec dies to where it is visible in the filler tube. That way I am certain that the variance in fuel amount is minimized. The trip computer is usually within a half mile to two per gallon and mine says 33.1 after 13K miles since reset.

wotbill

I just chose the variable of potentially underfilling the tank as compared to the previous fuel stop (which would give the highest result) vs "overfilling" (which would have made the difference between calculated vs indicated economy even greater).

Of course, the error in calculating FE gets reduced with a more repeatable fill (i.e., up to the filler neck) but the point my fuel fill "sensitivity" study showed the range of possible calculated FE with +1, -1 gallon still didn't approach the indicated values. In fact, I would have had to underfuel by a bit over 2 gallons as compared to where the pump actually shut off) to approach the indicated values, which is unlikely.

I don't want to rely on just leaving the "reset" value running since long term running average is a numerical filter which cuts out the high end and low end values. I'm interested in the economy of each tankful.

However, to your point, my next step is to fill the vehicle up to the neck and see where the fuel economy calculates out when the fill-to-fill variation is on the order of a pint or less.

ImInPA

The filler neck alone is over a gallon. I have never seen a trip computer that was 100% accurate. They are almost always a bit optimistic at the pump. In any event, I hope you find this to be your biggest complaint with your car.

Arrie

I think the computer in car does not register undriven time the engine runs, i.e. when the engine runs but car is not moving the fuel is used but this is not calculated in the fuel consumption. This means in city driving with lots of idle at traffic lights the actual gas mileage is far less than what computer shows. You get displayed value close to real value only with highway driving that has virtually no idle time.

El Cid

MPG will probably vary a lot until you get 1,000 miles on it.
My experience has been that the computer in the car shows slightly less than what I get when I use the old fill it all the way up and use odometer and numbers of gals. method.
It is very hard to get exactly the same amount of gas in a vehicle every time. Lot depends on pump being used and some even say time of day.

ImInPA

In mine, If I come to a stop, I can see the mpg's dropping. In mine, it most definitely factors in when a vehicle is at a stop.

listerone

There are several points I could make here to the OP but the main one is that everything I've read...and my *own* experience with diesels (30K miles on my BMW diesel)...suggests that a diesel's fuel economy increases noticeably as it gets a few miles on the clock.So,IMO,one should only start doing detailed mileage calculations once you've got,say,10K miles on the odometer.

Just my 2 cents' worth....

Arrie

[quote=ImInPA;4667446]In mine, If I come to a stop, I can see the mpg's dropping. In mine, it most definitely factors in when a vehicle is at a


You see the estimated available miles left with the fuel in the tank dropping. This is not the same as fuel mileage calculation.

I have noticed that when I drive a full tank straight on highway (yes, have done it several times) and stopping only for a cup of coffee or a small snack my displayed fuel mileage is within 0.5 MPG compared to calculated value from filled gas and driven miles.

Comparing this to a Chevy Tahoe that I had in the past is poor as the Tahoe showed very accurate MPG values with both highway and city driving.

I learned in an Audi forum that Audi's don't count undriven miles to the MPG values, only engine running time when car actually moves. I would not be surpriced if MB did the same thing. At least my car seems to do it.

ImInPA

[quote=Arrie;4667782] Actually I see the MPGs dropping at a stop. It is a different screen than the screen that shows miles to empty. On my car, as well as every car I have ever owned with at trip computer, stop time with engine running, is part part of the calculation. Now, please keep in mind that my E350 Bluetec is somewhat different than others: Mine has a really great ride, good handling, high quality interior materials, the solidity of a tank, working bluetooth, audio streaming, phenomenal fuel economy, "just right" interior lighting, more than adequate storage space(s), and no real or reasonable nits to pick. After all..."they promised me a Mercedes Benz"...

golfster

[quote=ImInPA;4668010]^ I like that!

Arrie

[quote=ImInPA;4668010]
Mine is a lot like yours. The only difference seems to be the engine as mine is a gasoline version.

K-A

[QUOTE=ImInPA;4668010]That's awesome.

To quote ol' money bags Warren Buffet: "The HAPPIEST people DO NOT necessarily have the BEST THINGS, they simply APPRECIATE the things they have".

El Cid

One consideration is that the odometer on dash is correct for calculating MPG when comparing to the computer doing it.

dis6933

Hi

I have purchased this vehicle used and have filled my tank 4 times.
I record all my consumption on a spread sheet, which calculates the mileage actual and I record the MPG since reset shown on the display. I reset the MPG display at each refueling.
My findings are that the displayed numbers are more that 10% optimistic.
Here are my numbers for the last 4 refills:
24 MPG calculated vs. 27 MPG displayed; 25 vs. 29, 30.5 vs. 33.3, 26 vs. 29.

In my gasoline SL and S, the numbers are within 1 MPG.

Is there any fix for this?

Don

El Cid

I "tested" my car when I first got it and found over the course of several fill-ups that the onboard computer read lower than actual.
However, it is actually impossible to acturately determine exact fuel efficiency by filling tank, recording mileage, etc. Way too many variables, such as how much pump actually dispensed each time, was tank filled to exactly the same level every time, did you drive the exact same route at exact same speeds and exact same number of slow downs, speed ups and stops, temperatures, etc.?
Another problem, at least with mine, is that when I reset the computer, it defaults to 22 MPG to start calculating, even if I am going down a hill with foot off accelerator.
The automotive magazines and Consumer Reports measure it with special devices over same courses.

dbldpr

I have not figured out how to get the mpg on the dash yet. But I put 6 gallons in the car and went 123 miles of stop go city driving. I thought that was pretty good compared to the 10 mpg my 2009 envoy gets. Bought the car in December 2013 and I have about 400 miles on it now. Waiting to go on vacation so I can see what type of milage I get on the highway. Love the car but hate the eco button.

GoBlando

In my Turbo E550, I have noticed a pattern. When I first got the car, the display was always optimistic by 2mpg (+/- 0.1). About 3k miles ago, I had a check engine light on and they ended up replacing all the MAF sensors in the car and reprogramming it. Ever since then it has been all over the board. Sometimes it is precisely accurate, other times it is +2mpg and anything in between.

I am starting to wonder if the calculation is based on a specific percentage of ethanol. I am going to try and use the same pump at the three gas stations I use and do a three tank average at each of them to try and establish a pattern. If one exists, it will give me some clue that it is a gas quality problem and not an engine, sensor, software problem (though that is probably it).

mikemargolis

2011 E-350 Bluetec.

I reset the second mileage meter at each oil change.



Right now, I have 59,000 miles on the car, and 8670 miles since the last reset. It is reading 35.6mpg on the dashboard.

I use fuelly.com and am quite careful to record each tank. Over 31,000 miles and 69 fill ups, my calculated mileage is 30.7mpg.

I can see a small difference between the two, but obviously fuelly is correct: averaging over 70 tanks and 30,000 miles. But a delta of 4.9mpg is a 14% error!

This leads me to believe that the dashboard mpg meter is absolutely positively not worth a d@mn.

thefisch

I have had the same inaccuracy on other cars from other makers. 10% sounds about right. If these were more accurate, more folks would complain about real mpg versus 'promised' EPA mileage. Ignorance is bliss. Of course the higher the mpg the greater the mpg difference. Seems more accurate when you get 15mpg as compared to 40+. One benefit of having a gas guzzler.

thenew3

On my previous VW and Audi vehicles, I had a VAG-COM cable that I could use to connect to the OBC and modify the fuel consumption ratio. Doing that over several tanks will get the MFD estimated MPG to be within 0.2 mpg of actual.

Not sure if there is such a device for MB. but on my E350, over the last 7500 miles, I've found the MFD is about 0.0-0.5 MPG higher than measured at the pump. I think 0.5 MPG is well within the margin of error. Not sure why you guys are so far off.

dis6933

HI to all

This discussion has gone all over the map, but for the most part it appears that the average error on the E350 Bluetech is 15% optimistic.

The real question is: CAN THIS BE ADJUSTED?

ANY ONE BEEN TO THE DEALER AND ASKED THAT QUESTIONS?

THANKS

dis6933

What a shame!!!!


Subject
My fuel consumption indicator is optimistic by 15% over many tank fills. This...

Response By Email (Nadia M.) (05/19/2014 03:19 PM)
Dear DS,

Thank you for your email to Mercedes-Benz USA.

There isn't an adjustment that can be made for the consumption indicator.

We appreciate the opportunity to respond.

Sincerely,

Nadia M.
Mercedes-Benz USA
(800) 367-6372

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Customer By CSS Web () (05/17/2014 02:36 AM)
My fuel consumption indicator is optimistic by 15% over many tank fills. This is a E350 BlueTech 2012.

My SL500 and S430 are accurate to about 1%.

Can this be adjusted?

THanks