mtrevelino

I just returned from a 2,300 mile trip. I filled up four times. As to my subject title, my first and last fill ups were steady driving. My instrument panel mpg gauge showed 42.4. When I filled up, my cdi took 19 gallons, while I traveled 652 miles. That comes out to 34.3 mpg, not what the instrument gauge showed. My last tank was about the same, I went 631 miles on 18.8 gallons of diesel, which averaged out to 34.4 mpg, not 41.4 the instrument gauge showed.
I always thought the instrument mpg gauge was more accurate than that?
I cannot complain because the car performed flawlessly. I have 143k miles on my cdi. For my next tire change, I may replace some front suspension parts. I do hear a slight creak (crunch) the first time I back out of the driveway with the wheels turned slightly. I had the lower ball joints replaced at 50k. My cdi seems to drift some while going down the highway, but it always did that. My other concern is the water pump and of course the sbc.
Thanks for listening!
Mike T.

kajtek1

1. Each gauge in this World require calibration
2. My gauges on W211 did show quite accurate. Usually within 3%, while on Bluetec I did have fillups in the row, showing higher calculated mpg, than the reset I did at every fill up.
3. Those tanks have pretty odd shape and slight fueling pad slope can make quite a different in air bubble left in the tank.
Meaning don't take anything really seriously unless you have at least 3 fill-ups average.

mtrevelino

Every morning when I start my cdi, the instrument cluster mpg resets. Also the miles driven that day and hours driven reset. So by this, the mpg gauge and what I actually get are two different things, especially if I travel over 500 miles in a day with cruise control set at approximately 78 mph.
If I cycle further into the menu, I get the overall mileage, hours, and mpg. This mpg shows somewhere in the 34 mpg range, but that may be a range of 17k miles. The last time that reset was when I replaced the main battery.
Mike T.

kajtek1

You have
"since start up" meter, that resets after I remember 5 hr of parking and
"since reset" meter, that can hold mileage and mpg for several fill ups.
All you need to do is keep receipt how many gallons you put in the mean time and this way you can compare long-term computer calculation with hard numbers on paper.
To top it you have so-called daily meter at the bottom where you can reset miles per your wish.
Lot of displays to play with.

mtrevelino

I do keep a detailed Excel spreadsheet of all my maintenance plus fuel mileage. The best my cdi got was 38.3 mpg (going 593 miles on 15.5 gallons). The worst was 28mpg (going 508 miles on 18 gallons). The funny thing is that I got better mileage using winter blend diesel during February, and the worst mileage during July. My average on my spreadsheet is 32.5 mpg.
I keep hearing all these stories of people getting in the lower 40's, but I do not know how that is happening, unless they are doing 60 mph with cruise set.
Mike T.

mtrevelino

Not to keep from going back and forth, but today I noticed that my trip meter was at 613 miles. I know that I reset it after filling up. I filled up two days ago, and yesterday it was reading correctly (around 50 miles on it), so something happened between yesterday and today that made it revert. I think this is the third time it has happened. I usually watch the trip meter as I can go between 500 to 560 miles of local driving.
I know what happened! Yesterday I reset (clear) the service reminder, this must have made it go back to its prior setting. I think this has happened each time I have to reset the service reminder.

Carsy

Please see attachments.

4.9 l /100 km equals 48 US MPG

5.3 l /100 km equals 44.38 US MPG over 642 miles range .Note still 1/8 of a tank left & no fuel low warning lamp illuminated.

kajtek1

Speed, speed, speed.
That is what makes huge difference in mpg on properly running engine.
Those are historic to me pictures, when about 8 years ago I was killing boredom on Nebraska freeway.
The last one was taken in Utah and not suppose to be taken seriously as the display is end of the scale and not showing the actual readout.

mikemargolis

The dashboard meter is notoriously inaccurate.

I used fuelly.com for a long time (more than 50,000 miles), now I got lazy and don't anymore.

I have also seen 42+ mpg on the dash, and if you click below on my fuelly banner, you'll see that I've never broken 40mpg on one tank.

Lesson is: don't trust the guess-o-meter, trust the math that you do with miles and gallons, or kms and liters.

Nonetheless, 700+ miles on a single tank is amazing.

listerone

Can't recall ever having done careful mileage calculations with either my first BMW or my Bluetec.However,I have done so with my current BMW.Using summer diesel my the dashboard reading on my "d" is usually close to 60mpg at a steady (cruise control) 66mph.But on a fillup-to-fillup basis for the same trip I can get around 53mpg.

rapidoxidation

I'll consider myself lucky that my dash meter is pretty much dead nuts on.

Diesel #2

I have hand calculated about 5 times, and all 5 times the dash has been off by 2-3 mpg. I, much similar the OP average about 625 miles and usually fill up about 18.5 gallons. So realistically im getting around 33 mpg with city and highway driving. I do have a heavy foot and the torque is great in Sport mode. Im sure if i accelrate a bit slower from red lights and drop highway speeds from 75mph to 70mph, i probably would get around 36-38 mpg. To be honest, anything around 30mpg or above is more than fine with me.

mtrevelino

Thanks for all the replies and feedback. At lest my fuel gauge is accurate. And since I reset the trip computer I know that I can go 500 miles on average on a tank of fuel. I just wish the mpg meter was more accurate.
Mike T.

kajtek1

Let me repeat.
All gauges do require calibration.
I have 4 thermometers in my house and each one shows different temperature.
But once you calculate the error margin, it is smooth sailing down the road.

marc hanna

One thing that I think affects the precision of the fuel economy reading is whether or not you have had an injector replaced, and whether or not the new serial # was input into the ECU. When I switched out an injector, I was getting the same real-work economy, but the gage was no longer accurate - it went from a 2% error to about a 10% error.

I have not verified that this can affect the reading with any technicians or experts however.

kajtek1

I am skeptic about programming new injectors, or air filter replacement on those cars.
There is program, but I ignored it when I changed air filters for few weeks and later resetting did not do any change.
Than my filters were packed up to covers with insects, that added 2 sec. to 0-60 acceleration time, yet the computer did not react.
I think just like the old myth about FSS actually testing the oil, it is lot of BS.

mtrevelino

All I know is that mine must be off by at least 20-percent. When I fill up after a 600 mile road trip and calculate that I got 34mpg, and the digital readout states 42mpg, that is approximately a 20-pecent difference.
If I am doing local errands, the digital readout will start out at approximately 26mpg and gradually rise. Based on the 20-perecnt inaccuracy, I would be getting approximately 22mpg actual mileage around town.
Again, to be getting 34mpg on the highway in a e-class, is not a bad thing. I just wish the digital gauge was more accurate.
I do not care that it is off (I guess I do care (LOL)), I was just commenting on how inaccurate it is.
Mike T.

dieselfan1974

One thing that you should consider is the cetane level of your diesel fuel. I have been driving a diesel for several years and have determined there is a huge range in the cetane levels in diesel fuel sold in the USA. I have found BP to have the most consistent cetane number which usually ranges 49-50. The stations don't post the cetane levels, however I believe the minimum requirement in the USA is 43.

DanD.

I found thus table a long time ago

Cetane Diesel-Marken:
BP (Amoco branded), 51
Chevron, 49 (51 with Techron D)
ConocoPhillips, 48 (California 48-53)
PetroCanada, 47-51
Shell, 46;
Sinclair, 46
Marathon 45
Exxon/Mobile, 43-46
BP, 40-42 (Powerblend 47)
HESS, 40-45
Husky, 40 (Max 41-45)
Sunoco, 40 (Sunoco Gold 45)
Holiday Stations, 40-43
Love's: 40
Pilot: 40
Valero: 40
Sheetz: 40
Flying J, 40

kajtek1

Funny you find the chart showing differences, when it was proven lot of times that all those brands take the fuel from the same refinery, what would be the closest around.
When Shell and Chevron claim they add detergent into the tanker (nobody have seen them) - the cetane can't be adjusted by additive. It does come from refinery.

marc hanna

Not to be standoffish or anything, but cetane number can be adjusted with additive. The most common cetane booster is 2-EHN. This is clearly demonstrated in the study the was published by Sandia National Laboratories in 1998: The Effects of 2-Ethylhexyl Nitrate on Diesel Spray Processes.

For information on Sandia:
https://en.wikipedia.org/wiki/Sandia...l_Laboratories

I agree with the rest of your comments regarding the tanker filling depots.

kajtek1

I stand corrected. Cetane can be changed with additives, but what it would take to change it in significant number on fuel in the tanker?
Once again, how often you see Shell or Chevron tanker with driver carrying bucket with additives up and down the ladder?

marc hanna

The treatment rate is 250:1 to raise the cetane number 10 points. So far the best commercially available product I have found is Opti-lube's "Boost" which is formulated at 70%+ 2-EHN. So on a 70L fill (7/8 of a tank for an R-class or E-class), you would need 400mL of Boost. The cost is typically about $4CAD per tank (landed cost).

At a 10 point increase, you can ensure that no matter where you fill up you will meet or exceed the theoretical optimum for which the engines were designed for. In some cases you will exceed that, but there is no detriment to putting too much 2-EHN in, except the added cost.

It will be hard to measure fuel savings on a single vehicle because so many factors come into play that affect fuel economy, but the key measurable difference is the frequency of DPF regens, which will likely drop to 1/3 of their non-additive frequency. So for those who are concerned about the cost of a DPF replacement, the added cost of additive might be justified on that aspect alone.

I know all this because I spent a great deal of time building a business model around it for commercial vehicles. In the end, no one keeps their vehicles long enough anymore to justify the added cost, and for used trucks the damage is already done. At any rate, for those people who plan on keeping their diesel for a long time, cetane improver and lubricity improver is a definite asset for engine and emissions system longevity.

kajtek1

Our BT just turned 180,000 miles. Shall I start using the additives now?
Funny you mention so many variables.
On last 560 miles trip I filled up half-way with B20.
B20 per all the theory should lower mpg, yet my BT record increase.
That was the time when I was pulling trailer with CC set firmly at 65 mph and driving flat California valley.
The only variable could be wind.