Bad W123 Gas mileage

[Gil]

I'm getting crappy (21/25) mileage in my 84 300CD lately. Everyone else seems to be doing better than this. What steps can I take to improve these figures?


Gil

[Holson Adi]

It's probably the winter fuel or something? I read somewhere in this forum about this. Winter fuel has less energy / unit volume or something?

[jas2wa]

I just got 25 mpg on a tank in my 84 300TD and was jumping for joy... should I be expecting better mileage? What did your 300CD used to get?

[ck42]

If you're getting 24/25'ish around town, you're right smack in the middle of averagedom

I get ~24 and ~30Hwy.

Chris
'85 300SD

[GregS]

Your figures are right on. My '84 300D (California version) consistently gets 23 mpg.

To confirm this, check out your car at www.fueleconomy.gov

Greg
'84 300D, 170k

[Joe Blowe]

Originally posted by GregS
Your figures are right on. My '84 300D (California version) consistently gets 23 mpg.

To confirm this, check out your car at www.fueleconomy.gov

WOW! just checked the milage for the '85 wagon (the earliest they go back):

http://www.fueleconomy.gov/feg/2001cartablef.jsp?id=655

the california model is only rated 21 in the city, 22 on the highway, and 22 combined. i didn't realize it was that bad...

i've been getting 22 ~ 23 in the city, and have been kicking myself for getting such low numbers compared to others on this board. now i feel much better!

Joe
1982 *California* 300TD-T

[Gil]

I guess I'm doing ok, then.

I don't know why I've read so many posts and other bits about the 300D models getting 30 mpg highway. This must be another urban legend. I've NEVER gotten that much MPG before. I get 27 every now and then on the highway, but that's it.

Around town, I kinda had the idea I could do better than 21 MPG, but I gather this is about average too.

I get this no matter where I buy fuel, winter or summer.

Anybody out there get superduper mileage with their 123 diesel?

Gil

[GregS]

I think claims of 30mpg on a 300D come from either:

-urban legend
-inaccurate odometers
-poor math skills
-bragging/lying (whatever you want to call it)

Supposedly the 300SD will get better mileage. From my experience driving an SD I guess it comes from the fact that they have higher gearing. On the highway the engine spins about 500rpm lower for a given speed than my car does. This would definitely affect gas mileage.

Greg
'84 300D

In the winter I tend to get between 20-22mpg and rest of the year I get around 26 mpg.

[The Warden]

FWIW, I've been averaging 25 to 26 with my '85...but I remember hearing that '85's had higher gearing than other turbos (most turbos have 3.07 rear gears; I think '85 have 2.??'s)...

I can't complain, but I have to admit that the '03 Jetta TDi that i drove yesterday did quite well for a vehicle that gets 45mpg on a bad day. No I'm not thinking about replacing the Benz; my mom wants a Jetta and I'm trying to convince her to go diesel...

[Mike123]

I get 28-30 mpg on the highway, 25-26 in town, and 26-29 in mixed driving with an '81 300CD. My odometer is correct. I've checked it against the course set up by the state south of Columbus. I know at least two others who get appr. the same mileage. I do not drive more that 4 miles an hour over highway speed limit (about 59 mph) and do not exceed the interstate limit (65).

But, the bad news is that with winter formulated fuel I lose about 2 miles to the gallon and so do my friends.

I think that puts all of us in about the same general area.

[JHZR2]

In my 83, I get 'around town' milage of 24-25 mpg, and on highway trips it varies from ~26.5 (fast driving with AC) to ~30 more controlled driving with no AC.
My low over the past 20k miles was 24.23 and my high was 31.15

Winter (#1 diesel) can definitely kill your milage a bit, from what I have read, especially if you try to drive the car like it has #2 diesel in it.

On the other hand, despite being super cold out, make sure things are all within good working order. Since you say that youve been getting this regardless of time of year, I assume that it has been this way perhaps for years now. I was first going to say to change your air filter. But Id assume you have done that without seeing any change. I would perhaps check that your fuel cap seals well to the filler neck, and that your rubber fuel lines are tight as well (I used to get seepage from the cigar hose, dont think it effected my MPG, but I caught it early). Injectors can also be leaky. I notice that diesel fuel must seep out of the connections where the injection lines go into the prechamber, as there is always a funny film, not resembling spilled or leaked motor oil, around the inlet lines. DOnt knwo how much comes out, but some must seep there too. All sorts of tiny little things can add up to a few MPG

I dont know about if this could be the reason, but I would also say to get your transmission fluid/filter and your differential fluid changed. As I understand it, except in direct-drive gears (which our 4th may be), there is always some friction between the gear teeth, which may effect your milage a bit. Id also look into your wheel bearings (perhaps youve lost some of the grease packing so they arent spinning as well), and also check for a stuck caliper dragging a pad slightly.

Also, do you carry a lot of stuff in your car? added weight, underinflated tires, etc., can effect MPG.

Those are the things that passed through my mind if I noticed my MPG going a bit south. Im sure there are other things that it could be as well.
Good luck, hope you can squeeze a few extra MPG. If not, and your engines healthy, I wouldnt worry about it too much though.
Have fun with your car, I'd love to someday have a later model 123 CD They are such nice cars.

JMH

[84300DT]

back in october i did a 232 mile all highway run and got 27.95mpg.

but lately i've lost about 4mpg due to winter fuel.

[can-do]

Greetings All,

I think most mileage we post here per gallon has quite a few variables that to be consistant between owners there would most likely need to be a chart that would contain mileage of engine, turbo vs. non-turbo, dino vs. synthetic oil used, heavy foot, excessive idling, distance driven and driving terrain. Even mine on the '84 300SD varies one or two miles per gallon depending on what I did between fill-ups. I'd say an average range would fall somewhere between 22-28mpg depending on Calif. engine vs. Federal and of course all the above mentioned items. I think one of the most important things a diesel owner can do is track your own mileage on a fill-up to fill-up basis and track to see when the trend drastically drops off. This might be your best indicator over time that something isn't quite right if performance fails along with this dropping trend. Mine generally runs on the average from 26.4 to 27.7 driving the same roads every day.

Just my thoughts,

Charles

[Gil]

I just went to that web site on fuel economy. Pretty informative, though I was a little shocked a the propaganda meter labeled "Global Warming". It supposedly tells me how much "greenhouse gas" I pollute with my car.

Don't get me wrong, I know the stuff coming out of the tail pipe isn't exactly healthy, but spare me the guilt trip about how I'm killing the planet, already. There's plenty of strong evidence to the contrary that the earth isn't getting warmer anyway, and what little data suggest that it is warming is specious at best.

But this isn't really even the point.

Theories are fine, but I don't like seeing a government site spewing half truths and conjecture about how much the earth is dying and how I'm to blame. If Greenpeace (the same people warning us about global COOLING back in the 1970s) wants to use their donor's money to tell me this, fine. However, a taxpayer funded site really isn't the place for this type of lobbying posing as fact.


Sorry, but I had to let that out.

Other than that, it's a handy quick reference site for gas mileage.


Gil