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Mercedes 300D Suggestions



  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    That's a lot of miles. And it is not "common" for ANY car to go 400K--that is the extreme end of the bell curve and statistically unlikely. So don't count on that any more than you should count on living to be 105----you might, but most don't :P

    I'd say the average life of a 300 series diesel is about 250,000 with good care and presuming no engine/trans replacements or major restoration (after all, you can keep any car running forever if you pay enough). If you don't think so, go to a wrecking yard and read odometers. What better way to get some good data?

    So you are buying a car in the...okay, let's be generous...last third of its life.

    What do I think it's REALLY worth? About $6,500. What is the most you should pay? If you really have to have it, and it checks out GREAT, and you haven't seen anything nicer, then maybe up to $7,500. After that, you are over the market and on your own...your call.

    Remember---whatever gets you INTO a car cheap at the time you buy will come back to haunt you if you want to unload it. So if you don't like the car in 6 months, it'll have over 200K on it which makes it a hard sell for top dollar.

    If this car had 75,000 miles it could bring $8,500 or better, say from a dealer's lot with a financing provision.

    It does look clean, though, I'll say that. I don't know about the guy's story though. you could do a CARFAX report and check his mileage claims over the last 4 years. And "highway" miles is a meaningless term in some ways. Miles are miles when it comes to market value.


  • I just can't seem to stop this fuel leak at the main fuel filter housing on my '82 300D turbo.
    I changed the fuel filter- replaced the aftermarket with a MB from dealer.
    I put a new metal seal between housing and the bolt (that screws into the filter).
    Also, put a new rubber seal on the hollow bolt that screws into the filter (this rubber seal is in the stem of the main bolt).
    I bled the air by loosening the hollow bolt that goes out of the housing.
    (Haven't touched the bolt that comes back into the housing).
    Still have fuel leaking from under the top of the main bolt that screws into the fuel filter. after driving 3 miles.
    I don't remember seeing any leaks before I changed the fuel filter. And I can see now the difference in the diesel consumption- the gauge needle drops down faster.
    Is there anything else I should look at? It was supposed to be a simple fuel filter change!!
    Thanks for any help.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    That's weird. Maybe you can find a neophrene seal that will fit around the bolt. do you think you might have tightened down too hard?


  • No, I don't think I tightened too hard. With the old seal, i did tighten hard, thinking that would help. When it didn't, I got a new seal and noticed it was thicker than the old one, and it's brass- so I knew it was soft; hence took extra care not to tighten too hard.
    Maybe I should run a very fine sand paper on the housing surface where the metal seal sits?
    I cannot think of anything else, and I wanted to make sure there wasn't any other "trick" associated with changing the fuel filter. Is there anything else I need to be aware of?
  • I have a 1981 300d it is not a turbo. I am having a problem with the air conditioner. What could be making the fuse for the air conditioner keep blowing. I have had to change it several times.
  • samgm2samgm2 Posts: 14
    I have a 1985 300D that maybe having problems with the climate control switch (perhaps its something else). The usually does not come on. I believed the problem was in the climate control switch and took it apart and tested all the relays by applying 12 V to the circuit board as necessary and what I could of the switches. I also cleaned the contacts. Everything seemed to be in order with a cursory check with a multimeter but still no go.

    I do get heat ( not that I want it in the summer, but only as a result of natural air flow if the vent is open). No AC, no blower, no defrost.

    Anyone have a clue what direction I can take now. The maintainance manual refers to a diagnostic tool that I don't have for trouble shooting the system.

  • here's a website that I found recently that should help.
  • Well- this problem is now solved. The metal washer needed to seat better on the housing. I sanded the housing top lightly with very fine sand paper (waterpaper) to get rid of the little build up and a very small protrusion; reseated the washer and hollow bolt- voila! drove 50 miles without fuel leakage. I guess every small bit must fit properly!
  • jnicoljnicol Posts: 5
    I took my 82 330D in and had the transmission flushed. It was running great. Went to pick up the car and it wouldn't start. It sputtered and blew a cloud of black smoke and then just turned over and over. Brought my 300SD to it and tried jumping it. I fiddled for about an hour looking for vacuum leaks and whatever I could see. Oddly after about an hour of cranking on and off it started and ran great. I drove it home, turned it off, restarted it no problem and left it over night. The next morning the same problem.

    I changed the fuel filters, reprimed it, pulled the glow plugs and checked resistance all about 1 ohm, took the glow plug relay out of the 300SD and popped it in - still won't start. Took a rag and dipped it in gasoline and put it inside the air cleaner (outside of the filter - eventually got it going - it ran great. Next morning it won't start.

    The glow plug light comes on for about 3 seconds and goes out normally. There is no smoke at all coming out of the exhaust while it's cranking.

    I'm out of ideas. Could the transmission shop have knocked something loose that's causing this problem? Could it be a bad fuel pump, injector pump...? How can I tell? Any help or suggestions will be most welcome.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    Oh your glow plug should stay on longer than that on a cold engine. I think you need to replace the glow plugs if in fact the engine runs great but won't start. You should replace the glow plugs every 2-3 years anyway.


  • I had the same problem with my 83 300D. Check the black rectangle shaped box that is mounted on the drivers side from fender under the hood, should be located near the front of the fender. There is a small metal link(fuse) that is held in place by 2 screws. This is a fuse to the glow plugs. The time I had that problem, this was the solution, if it blown, you will be able to see this right away. BTW you will need to remove the cover on the box to see the fuse.

    Ken Sharpe :surprise:
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    Yeah I was wondering about that fuse link (80 amp?) but then I wasn't sure if the glow plug light would even light.

    But anyway, good idea to check that...although blowing 80 amps is a kind of scary did THAT happen?

    I have a test you might try but you have to be very can activate just ONE glow plug with a battery jumper cable and see if the engine kicks off...but you have to be very careful not to ground the battery cable to anything metal except the tip of the plug....tricky...I used to do this test by wrapping very heavy gauge wire around the glow plug and then attaching the jumper cable to that, maybe one foot out of harm's way.


  • What kind of mileage is expected for a 300D? I am getting 25mpg on the highway with my 82 300D turbo. I was expecting around 28. Anyway to improve it?
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    25 is pretty darn good, you can't do much better than that unless you want to start driving in a very silly way. Remember you have a very heavy car shaped like a brick--you can't fight aerodynamics unless you want to do something radical to the car or drive more slowly and cautiously.

    I suppose you could inflate your tires more and carry less fuel and get a 4-wheel alignment---all those things might....MIGHT...gain you 1 mpg.


  • Just trying to squeeze every little mile- at todays gas prices!! I guess I should be happy with 25. I drive normal, and absolutely love the feel of the car.
    I did one very very stupid thing recently, though. While changing fuel filters and checking for leaks, I did not latch the hood down tight, and drove in my sub- Well, the wind opened up the hood, and one hinge got twisted a tiny weeny bit, and so now when I close the hood, there is a slight intereference on the passenger side near the windshield side.
    Would a body shop be able to set it straight?
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    Yeah, a body shop might be able to help you---it rather depends on what got bent and where.

    As for better MPG, you might also try synthetic oil, although I'm a bit wary recommending synthetic oil on a car that is very old.


  • At my last oil change- about 700 miles ago- I did put Pennzoil synthetic and dumped a bottle of the Lucas cleaner in the tank. I can feel the difference- it runs much smoother and I think the diesel noise inside the car is lower. You can just get that feeling of a well oiled powerful machine purring along!
    Yesterday my driver side window stopped working, Previously, for a rear window it was the fuse- I'll check fuse again for this one also, but do the switches or motor have a tendency to go bad?
  • jnicoljnicol Posts: 5
    Thanks for the good advice, everyone. I have a followup question or two.

    1. No one commented on the glow plug resistance. Shouldn't I be able to spot a bad glow plug in this way? I'm wondering if it might be a bad wiring harness also. I'm still wondering if something may have happened at the trans shop. I checked the 80 amp fuse and it's intact.
    2. Could clogged injectors or bad fuel pump cause this problem starting, yet allow the engine to run okay once it gets going?
    3. Should I use a glow plug reamer when I change the plugs?

    Thanks all!!!
  • Hey I got a 1976 Mercedes and im trying to change alternators..But i cant get to the top nut to loosen it so i can get the belt to loosen up.. Anyone have ne suggestions on how to do that??
  • Ok i got the alternator off and it is stuck under the hood like a mouse in a trap but does anyone have ne idea how i can get it out... From what we can see is we are going to haft to take out the air compressor to be able to fit it through the top..But to get that off it is looking like we are going to haft to take almost everything off to just get it out... So if you got ne ideas on what to do or know how plz tell me...TY!!!!
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