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  #1  
Old 01-01-2008, 09:40 PM
Benz'n'thusiast
 
Join Date: Jun 2006
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My fuel mileage to the tank can't be right...

Hey everyone..

I've got a 1987 300D with the OM603 in it, runs good- got a bit of an idle fluctuation problem and loooots of smoke on a cold start (some glowplugs are bad) but thats about all thats wrong with it. Since I bought the car in october from a mercedes garage, I averaged about 330 miles of fuel to a tank. However I noticed as it got colder out, I get approx 280 miles to a full tank- less sometimes. I don't know what the deal is with that, I thought it was normal! I read that other people were getting closer to 400 miles to the tank, and that would be astounding considering most of my driving is highway driving- 90 miles on the interstate 5 days a week. Usually cruising at a steady 80mph.


Can anyone point me in the right direction to correcting my fuel mileage? I'm a broke student and need to pinch every penny out of what I can

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  #2  
Old 01-01-2008, 09:51 PM
Unofficial wormcan opener
 
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Quote:
Originally Posted by easy_asW123 View Post
Hey everyone..

I've got a 1987 300D with the OM603 in it, runs good- got a bit of an idle fluctuation problem and loooots of smoke on a cold start (some glowplugs are bad) but thats about all thats wrong with it. Since I bought the car in october from a mercedes garage, I averaged about 330 miles of fuel to a tank. However I noticed as it got colder out, I get approx 280 miles to a full tank- less sometimes. I don't know what the deal is with that, I thought it was normal! I read that other people were getting closer to 400 miles to the tank, and that would be astounding considering most of my driving is highway driving- 90 miles on the interstate 5 days a week. Usually cruising at a steady 80mph.


Can anyone point me in the right direction to correcting my fuel mileage? I'm a broke student and need to pinch every penny out of what I can
A couple suggestions. First your mileage will be slightly lower in the winter. Try driving at 65mph for a tankful. When you are driving, pretend there is an egg between your foot and the accelerator pedal. Having said that. I have an extremely hard time taking my own advice, but when I do, my mileage will increase.
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  #3  
Old 01-01-2008, 10:09 PM
Benz'n'thusiast
 
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Ironic you say that, my mechanic explained that to me, he told me to pick a speed, cruise at a steady speed between 55-70 mph, and note my fuel mileage on one tank full. At 65-70mph I got 289 miles to my full tank. I believe thats around half of what people should normally get, correct?

I tried cruising at 65-70mph ish for a whole tank, and really really really babied the car and still couldn't really top 300. Where can I start to correct this? Some typical problems preventing these cars from getting proper fuel mileage?
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  #4  
Old 01-01-2008, 10:19 PM
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I was having the same problem.....then realized my odometer was slipping and was only showing about 250 miles for every 400 I traveled.
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  #5  
Old 01-01-2008, 10:26 PM
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Quote:
Originally Posted by rick surgent View Post
I was having the same problem.....then realized my odometer was slipping and was only showing about 250 miles for every 400 I traveled.
Well that is low then. Last tankful which was 50/50 city/highway I got 27mpg and I have the wagon and burn B50.

That's right the VDO odometers are known for that. You could check that on the interstate with the measured miles or use a GPS. When was your air filter last changed? How is your tire pressure? How is your acceleration? 0-60 should be around 11 seconds I believe.

Has the trap oxidizer recall been performed on your car?
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Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss
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  #6  
Old 01-01-2008, 10:37 PM
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It's the odometer

Quote:
Originally Posted by rick surgent View Post
I was having the same problem.....then realized my odometer was slipping and was only showing about 250 miles for every 400 I traveled.
I had the same problem with my '87 300DT W124/M603 car -- the odometer would work normally for awhile but then it would stop for a few miles, then start again. In about 200 miles it might register 140 or less or more. I finally had to do something when my wife reported getting 16 MPG! I "caught" it by putting a GPS in the car and comparing readings. Once I realized it was the odometer, I pulled the cluster and sent the speedo unit to Palo Alto Speedometer in California (under $200 ). They went all through it and it works great and my around-town mileage is now in the mid-20s.

It is also possible (and much less expensive) to fix the odometer yourself by carefully knurling the steel shaft with a pair of pliers or a vise. Then the plastic gear will make better contact with the shaft. It's a design flaw, really. Shame on VDO!

Jeremy
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Total. . . . . . . . . . . . 627,762
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  #7  
Old 01-01-2008, 10:41 PM
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Just thougt I'd throw this out there for discussion:

I was looking through the english language edition owners manual that came with my euro 84 300TD yesterday (covers all 123T models, 200T, 230TE, 280TE, 240TD, 300TD, and 300TD-T left and right hand drive models) and I came across some plots of fuel economy as a function of speed.

For a w123 300TD-T fuel economies were (in miles per US gallon):

"urban": 22.64

continuous operation at 56 mph: 29.39

continuous operation at 75 mph: 21.56



So, the differences you are observing between your milage at steady 80 mph operation and someone else's driving at "65 mph with an egg under your foot" are well within the expected range of fuel economies.

I knew that speed has a huge impact on fuel economy, but I didn't really appreciate how much. Its quite startling.

Having said that, I would agree with Rick. Check the odometer first.
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  #8  
Old 01-01-2008, 10:52 PM
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Quote:
Originally Posted by Douglas.Sherida View Post
Just thougt I'd throw this out there for discussion:

I was looking through the english language edition owners manual that came with my euro 84 300TD yesterday (covers all 123T models, 200T, 230TE, 280TE, 240TD, 300TD, and 300TD-T left and right hand drive models) and I came across some plots of fuel economy as a function of speed.

For a w123 300TD-T fuel economies were (in miles per US gallon):

"urban": 22.64

continuous operation at 56 mph: 29.39

continuous operation at 75 mph: 21.56



So, the differences you are observing between your milage at steady 80 mph operation and someone else's driving at "65 mph with an egg under your foot" are well within the expected range of fuel economies.

I knew that speed has a huge impact on fuel economy, but I didn't really appreciate how much. Its quite startling.

Having said that, I would agree with Rick. Check the odometer first.
Wow, if I did the math right, that is 35% better at 55.
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Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss
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  #9  
Old 01-01-2008, 10:59 PM
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Quote:
Originally Posted by Douglas.Sherida View Post
For a w123 300TD-T fuel economies were (in miles per US gallon):

"urban": 22.64

continuous operation at 56 mph: 29.39

continuous operation at 75 mph: 21.56
Once, when I was forced by a mechanical problem to drive a constant 60 MPH for 400 miles, my 123, complete with California trap cat and all, got 26 MPG. So the numbers are reasonable. As usual, it's the "nut behind the wheel" that makes the big difference.
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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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  #10  
Old 01-01-2008, 11:10 PM
Benz'n'thusiast
 
Join Date: Jun 2006
Location: new jersey
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The air filter is as dirty as a mofo and after work/before class I was going to pick up another one. I just got a GPS in my car so tomorrow I'm going to track my voyage to school with my TomTom and compare the numbers.


And that's indeed very interesting Douglas.Sheridia... cool find! Never knew it was that drastic.

But difficult to break 300 miles to a full tank doesn't sound correct from what I hear, especially with 75% highway driving..
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  #11  
Old 01-02-2008, 09:23 AM
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Really disappointed in old SPARKY's mileage till....

I found out the 15/16 miles per gallon I was getting was due to a slipping odometer gear. Then a mileage check confirmed that the odo was reading 12.3 miles for a 24.something miles trip. Re-did the math, and Sparky is getting between 30 and 32 miles per gallon in mixed freeway/town driving That just ain't half bad for a W126 5 cylinder full size car

When will Detroit wake up and put a good diesel in a family size sedan? Lots of folks would buy one. I've heard from several people that still buy Merican, that they would buy a diesel if they did not have to go overseas.

Regards

Run-Em
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  #12  
Old 01-02-2008, 10:01 AM
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clean air filter and properly adjusted tire pressure will make all the difference. If you want max mileage, run the tires at the highest PSI you can, for a more comfortable ride, less psi.
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  #13  
Old 01-02-2008, 11:15 AM
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It makes sense that the W123 is sensitive to highway speeds. The car has the aerodynamics of a brick. I usually return 27 highway at 70mph. My last trip back from Kansas I averaged 23 @ 85-90 mph.
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  #14  
Old 01-02-2008, 12:15 PM
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First you need to figure out your mileage. 280 miles to a tank means nothing, what does a W124 hold 21 gallons? Did you run it dry? Did you run it until a 1/4 is left? Chances are the fuel guage is off.

Next check the odometer with a GPS, its probably slow.
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  #15  
Old 01-02-2008, 12:39 PM
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that chart is interesting, but the OP is driving a 124, with a MUCH more efficient rear gear ratio and 6 cyl engine with MUCH more power and better fuel economy.
the 123 N/A vehicles had as high as 3.69 rear ratio, where the 124's with their clean 603 turbo motor and low 2.66 or so rear gear ratio get around 25 city and 35 highway. even at 80MPH...

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