I just purchased this '81 gold mercedes benz 300sd turbo diesel. I love it, it's got style and I'd like to think I can depend on it. Love that it runs on biodiesel. Not fond of the gas mileage because my last car was a '90 Honda civic dx hatch and I'm not thrilled with the mpg difference! Used to getting 35 now getting 25-28 at best.

I just put $950 if work into her, picked her up for $1500.
Replaced inject/nozzle return lines
Replaced cover gasket
Replaced drive belts
Replaced fuel filters
Replaced fuel primer pump
Replaced air filter housing mounts and mounting bracket
Replaced air filter
Replaced rear brake hoses
Replaced rear brake lines
Replaced fuel return lines
Replaced 5th injector plug
Replaced all 5 glow plugs
Full tune up

My problem now is that it sometimes has problems shifting into drive and one time it shifted out if drive in to neutral when I was already going about 35mph so I had to come to a stop and reshift.
I'm curious if this is a sign of a bad tranny needing replacement soon?
Also the left rear window occasionally won't roll up.
What did I get myself in to?
Also, what could I do to increase mpg?
Would it be really expensive to lube the sunroof in to working order?
I'm a 25 year old female and although I have a good job I'm not in any way made of money.
Thoughts?
Much appreciated!!

I would check the transmission fluid and make sure it isn't low on fluid. Needs to be checked with car at normal operating temperature, level ground, engine running, car in park with parking brake set. It may also be due for a fluid and filter change.

The MPGs you mentioned are excellent for a large heavy car, your 1981 300SD weighs as much as two 1990 Civic hatchbacks.

I am sure that more here that are more knowledgeable on these cars will chime in. Also, welcome to the site.

"25 to 28 mpg" is outstanding mpg for your SD. I drove an SD a decade and one half ago, so I can relate. My sunroof always worked perfectly in 305K miles. Mine's transmission always worked perfectly. I would change it's fluid every 50K miles, draining the torque converter every time as well. My rear windows required new metal/plastic lift parts at least once each. I replaced my glow plugs just once. I really enjoyed my SD, but that was almost 15 years ago that I sold it. They are potentially more problematic simply because of their age and usage or lack thereof over the decades.


Old used cars are just that - old and used. They require large amounts of parts replacements, parts fixes, and the labor in time and money to accomplish this work. All my vehicles are old and used, have lots of miles on them, and they all require occasional time and money poured into them. Just last week, I poured nearly $2K in parts/labor into my 14-year old E-Class diesel, getting it ready for it's new owners. That's the way it go. It costs money and time to own old used cars. It takes at times, a lot of time and money to keep them going. I prefer buying MB diesls used to new, and keeping them not over 10-15 years in their total age.

Although the MB car model you bought was known to give a lot of miles for little out-of-pocket for transportation needs over time.......the Wild Card of a car you now possess is now over 32 years of age. Anything, and everything can happen repairwise and parts failurewise to car that aged. Those are just the facts. To me, you have to love the car model to continue poouring money into the car you own. I love 'em, but have limits on the "pouring." I think it is realistic to expect you will spoend perhaps another couple three thousands of dollars getting it to be a reliable, and roadworthy motorcar. Only you, cam decide when to pull the life-support plug of continued money spending on a car.

One more thing........if you cannot get your 31 yr. old SD dependable enough to actually BE dependable, you're going to have to furnish yourself with alternate means of transportation. THAT, is why many have numerous old cars - something that will start when you need to get somewhere. As long as you have multiple cars, it shouldn't be too much of a problem, provided you keep them all in decent repair.

We're always here to help, or offer advice and opinions on these wonderful MBs.

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'06 E320 CDI
'17 Corvette Stingray Vert

I heard biodiesel lacks BTUs A Btu improver might help.I run Power Service my mileage is 29 to 30.However I have 215 70 14 back tires,and 205s up front,so my car sits higher in the rear.
Helps with the wind.Best interstate mileage is 32.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

Maybe you have bad engine or transmission mounts, or the shifter is out of alignment (yes it can happen and go into neutral) or the bushings are worn and it is not really in the position you think it is (fully engaged). There are a ton of things that COULD happen or be wrong on old cars, each car is different. Perhaps someone repaired the transmission in the past and not everything is lined up just perfect. You need to visit a Mercedes specialist that is honest for that kind of work and not just going to say you need a transmission replacement to start...
Fuel economy, you can get far more, adjust your driving to mimic a manual transmission, when you want it to shift (as early as possible) lift on the throttle so the transmission goes into the next gear, this way you can keep it below 2000rpm as much as possible, and stick to 55mph and you will see a great increase. Remember, in the early 80s 55mph was the speed limit and hence what manufacturers were aiming for highways cruising speed. They love cruising slow and reward greatly. There are other things that can be done to help, but it will cost money and unlikely to ever pay itself off in reduced costs, but changing your driving habits is free!

Maybe you have bad engine or transmission mounts, or the shifter is out of alignment (yes it can happen and go into neutral) or the bushings are worn and it is not really in the position you think it is (fully engaged). There are a ton of things that COULD happen or be wrong on old cars, each car is different. Perhaps someone repaired the transmission in the past and not everything is lined up just perfect. You need to visit a Mercedes specialist that is honest for that kind of work and not just going to say you need a transmission replacement to start...
Fuel economy, you can get far more, adjust your driving to mimic a manual transmission, when you want it to shift (as early as possible) lift on the throttle so the transmission goes into the next gear, this way you can keep it below 2000rpm as much as possible, and stick to 55mph and you will see a great increase. Remember, in the early 80s 55mph was the speed limit and hence what manufacturers were aiming for highways cruising speed. They love cruising slow and reward greatly. There are other things that can be done to help, but it will cost money and unlikely to ever pay itself off in reduced costs, but changing your driving habits is free!

turning up boost to 14 psi will help your mileage as getting rid of soot filled mufflers

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

What you've gotten yourself into Kenzi, is one of the greatest cars ever made for a total of under 3 grand. Sounds like a steal of a deal to me. But, I'm a 45 year old guy, not a 25 year old female who, from your description of your last car, and your age (no offence just stating facts) sound like someone whose used to newer cars that just work.

Your MPG's are excellent. Don't expect to improve them, it's not an economy car. Your rear window could be a switch problem. Does it manifest itself when operating it from the rear switch on the door as well as the one on the center console or just one of them? But you might need to tear into the back door and fix/replace the window mechanism.

Mercedes Benz does make a special lubricant specifically for lubricating sun roofs. I'd start with that and see how it goes.

As for the transmission. I'm not a mechanic so have no clue but it doesn't sound like a failing tranny to me. Not if you just put it back into D and it goes fine without jumping out of it again. Does sound like something might not be a aligned properly. Maybe just the shifter linkages need replacing etc. Also maybe the engine and transmission mounts.

As others have said. Old cars require maintenance. So do new ones actually, but most of that is disguised as "car payments". Only you can decide wether or not you like the car enough to do what's required to keep it in good condition.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Every time I think something bad is wrong with my SD, it turns out to be something simple. That said, I am not paying shop rates for labor and have extra cars for when it doesn't run. It usually runs and is more reliable than what could be bought for comparable dollars. Sometimes it doesn't run.

My intent is to give one of the SDs to my 11 yr old son when he learns to drive. My reasoning is that the car is safe and of low dollar value in case he bumps it. I'm also a reasonable father and realize hat he may not want an old car. In that case, he can buy any car that he wants - as long as he can pay cash, meet any of his other financial obligations and get it past his MaMa who also has his safety in mind.

I saw a badly wrecked SD and needed the piece that trips the door latch. All 4 doors opened and closed perfectly meaning that the passenger compartment was intact. Others have survived roll overs.

I'd keep it.

edit: Someone will know about jumping out of gear. New fluid fixes a lot and other things can be fixed without pulling the trans. I saw some good remans for not much money while looking to sell some Nissan trannys.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

The civic dx got 35 mpg vs the 25 of the 300SD because the civic weighed about as much as one of the doors on the 300SD.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Thanks everyone!!!
I have a great mechanic who has been working on Mercedes since the came off the line in Germany in 70's.
I think I will try to keep money set aside in case things go awry. I have been slow to sell the civic because I wanted it as a backup but I am moving 5 mins away from work and have been wanting to start biking more!
I'm thinking road trips aren't the best idea in the immediate future but maybe someday soon! I will talk with my mechanic about increasing mpg, tranny and sunroof.
He had mentioned the engine mounts needs replaced... Maybe they're the culprit?
You guys are great seriously. For those of us who don't know much and don't know anybody who does!

Congrats on your new car, and welcome to The Club. Seriously, these are great vehicles.

Engine mounts: A very common wear item. At that age, very reasonable that they'd be tired. I did mine many years ago - at about 200k miles. My car now has 400+k on it...

Tranny: Sure, yes. Diesels torque the heck out of their transmissions. You may need a new trans at some point, but...

As others have said: Check fluid first. Low level causing your symptoms is the first thing to check. With critically low level, car will absolutely not budge. Of course, locate the leak!

Another point: There is a very inexpensive (<$10?) bushing around the shift link to the transmission shift lever. It's a small PITA to install, but could easily account for all of your 'slipping out of gear' problems. I've gotta do this on my car, in fact.

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'83 300 SD
'05 E320 4Matic
'06 BMW 530 xi
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr