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Mercedes 300D Suggestions



  • MrShift@EdmundsMrShift@Edmunds Posts: 43,647
    Yes I'm sure he thought you were making a mistake.
  • dyates773dyates773 Posts: 24
    Please pass along to me a generous portion of sympathy for my decision today to buy my SECOND M/B Diesel. Just when my '79 300D needs absolutely no attention and the A/C is finally working I just jumped off a cliff today and bought a '87 300SDL. Bought it from a private owner who had it for 10+ years, lotsa service records, and the interior is great and the exterior fair. It has 207K miles, starts cold like a new car, and has many new parts. Two major issues: 1) The turbo doesn't appear to work 2) The A/C compressor cycles but in "Auto" the fan never turns on, in manual the blower comes on with heat only.

    Please share some advice on the turbo. What's the best approach? The reason I think its not working is it accelerates without that slight feeling of "boost" as the engine revs. Its as flat as my 300D with the A/C on. Is the Boost Pressure switch something to look into?

    With the A/C I know this car does not have the A/C Servo Unit my '79 has. The previous owner said an A/C Shop said the Pushbutton control Unit was bad. Any feedback would be appreciated.

    Well, there goes my free time for the next several months. (My wife says I'm a masochist!)
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,647
    Isn't there a boost gauge on this car?

    You got some real scary problems there pard.
  • dyates773dyates773 Posts: 24
    No boost gage.

    When I bought my '79 300D I had some similar scary problems. A little persistence and a lot of patience go along way. I try to look at the problems as being basic in nature and some are easy to fix. Just cleaning electrical contacts, replacing vacuum hoses/fittings, lubricating moving parts, changing all fluids/filters, makes a world of difference.

    I really enjoy the challenge as my project progresses. My '79 300D gave me a real sense of accomplishment as I worked on it. It now runs great, looks terrific, and is a joy to drive. My wife drives it everyday to work.

    I take great care in picking out a car. I give it a 100% inspection and a good test drive. Understanding how the previous owner treated it is HUGELY important. A good engine and a sound tranny are the keys. Shopping for parts saves big bucks.

    As always thanks for the feedback and I enjoy the forum.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,647
    Well you could have a stuck waste gate, or loose piping in the turbo plumbing, but really you need to find out if there is any boost at all. Can you determine if the turbo is even spinning anymore? If the turbo's shot, they can be sent out UPS to be rebuilt for maybe $400---it's not the end of the world. There's a place in Houston that I found in Road & Track magazine that did a nice job on my Saab turbo(s). Pain to get them in and out, but since you like projects, not so bad. I've done a few but not on a 300. Biggest challenge is getting the engine-baked rusty bolts off the turbo/exhaust system.

    You can also usually find climate control units on Ebay or through places like

    If you had vacuum leaks generally your engine would not shut off as I recall, as it bleeds the vacuum reservoir, but I'm not sure on your model whether the engine has that same vacuum shutoff mechanism as the earlier cars.
  • anasanas Posts: 7
    The newest posting on the site where the 1982 coupe was listed says it sold for $ is a crazy market in the Northwest!
  • burdawgburdawg Posts: 1,524
    If that's true then the new owner has my best wishes. What's the price for diesel per gallon around there?
  • anasanas Posts: 7
    It averages about $2.50.
  • My 82 300D was totalled by another driver in February, so I hastily purchased an 85 300SD that appeared to be in mint condition - the seller was moving back to Europe. $5,400 was probably high, but the leather was mint, so was EVERYTHING else. Well, first it was brake pads, new caliper, a leaking condensation (?) hose that made the carpet under the driver's seat get wet, broken plastic thing in the rear window, the RADIATOR, and 2 new tires (which I knew before I bought it that those had to be purchased). The AC worked great too. Till this weekend, it was in the 90's, and all it does is blow air. Not hot air, but "just" air. We nearly died. I can take it to the mechanic to spend hours looking for leak and fixing it - $$$$ - OR to a friend with a used car lot will put in some freon for a temporary fix. Might last for weeks or months, even. I'm just fed up to here spending money on repairs on this stupid car... it never lets up, and I'm in too deep to ditch the car. So I may as well ride it out and hope each repair is the last. Is there anything wrong with that plan? Anything I need to know, such as what KIND of freon, etc? It has now become a very expensive car, as you know. My old 300D didn't give me this much trouble!!
    Thanks for any answers.
  • burdawgburdawg Posts: 1,524
    Pretty much all of these things are normal maintenance items. Brakes, tires, etc will wear and need service, and replacing a radiator in a 20 year old car isn't very surprising.
    Unless it's been converted to R134, that year would use R12 freon. If you don't want the expense of having it tested and repaired then my gut feeling is to have it recharged and see how it does. If it stops working real soon then you know it has a major leak and needs major repairs. If it keeps working then it's probably a minor leak and you can charge it from time to time as needed (but more than likely it will only get worse). R12 freon isn't cheap, you need a license to buy it legally.
    Be aware that in many locations in the US it's illegal to recharge an R12 system that is KNOWN to be leaking. If you take it to a licensed shop then they will have to go through all the steps to insure that R12 isn't released into the atmosphere, which is where a lot of the cost comes in.
  • Thanks for your answer, Burdawg, I appreciate it. (I don't think the radiator was original, and actually I question whether the mechanic who fixed the condensation hose earlier that same day did it). Either way, I'm glad you have prepared me for the possibility of R12 freon. Yikes. All I know is that this car came with "California emissions controls" on it, that causes it to use more diesel per gallon than if it didn't have it. I told the seller that in Texas, diesels don't need to have that emission stuff on them, but apparently it was shipped from Germany to California (??) and came built like that. And that California was the strictest state regarding emission control. Now, whether that has anything to do with freon, I don't know, but maybe maybe it will take the cheaper freon??
    By the time I paid the tax & title and $1,000+ in these repairs, it has become too expensive to get rid of, and I'm hoping everything will let up and run problem-free for a year or so till I catch up. In hindsight, I wish I'd just bought a Ford pickup truck. My husband's has NEVER been in the shop in the 4 years we've been together. Between my old 300D and this one, I seem to always be needing a ride to/from work because the car is in the shop. I keep sayin' its cheaper than car payments, but maybe I am making some poor car choices just to have that 3-pointed star on the hood. I had the other car for 15 years.... I don't know any other vehicle that could have run for over 300,000 miles.
    Back to freon, I have a shade tree mechanic who is damn good, so I can get around quite a few things that way. I just wish it didn't require that problematic R12 freon.
  • Just for grins (me again), how much is the R12, approximately? Here in Texas a can of R134 is $10.99.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,647
    R12 is quite expensive....but it also works a lot better than the new stuff. Please don't put R12 in a leaky system BTW, and also be sure to check and see WHAT it is you have in your system. These don't mix, and some nuts even stuff propane in there to just get rid of a car.

    You might start off by checking to see if your AC compressor clutch is even working. If it isn't, you can start with that problem as it is the primary cause of your troubles.
  • gagricegagrice San DiegoPosts: 28,678
    If you live close to the Mexican border they do not charge a fraction for th R12 that is charged in the states. Find a good shop there to fix your air conditioning. I took an older car into Tijuana and found an AC shop that charged pennies on the dollar.
  • ellennbellennb Posts: 1
    greetings! mr. shiftright, I am offered to buy a ' 92 300(350?) diesel sedan from my boss for $2000. I drove the car for a month 1 1/2 years ago, after she bought it from a lil' ol' lady (very low mileage). My bosses' daughter drove it for a while (not badly), but now it is sitting in a shop needing repairs to the starting system and climate control. The shop mechanic hasn't been around to fix the car, so they just want to sell it.
    Now, it seems I had heard somewhere years ago that you have to have a/c running/working on a diesel engine or you''ll get big trouble after awhile. I kept telling them so whenever I saw the car, and next she was raising the hood to shut off the engine.(sheesh) I've got the gist of the problem from reading most of this site,lol, I couldn"t stand too much repair and would dread looking for the right mechanic (after dad, who could meet up!) Oh, and if I want to buy it, the bosses' husband will put a 'pulling lever thing" onto the starting-knob 'til it gets fixed. Hows that sound? Is this deal worth it? It is a beautiful car, I would love to get it, I just want to be able to get it right. ( I'm in socal)
  • burdawgburdawg Posts: 1,524
    Around $25 per 12oz can. Just check Ebay. R12 is still plentiful, but you need a license to buy it legally (in the US). Also it can be recycled. The regulations for use of R12 are not generally well understood by the public. I agree with Shifty. If you have an R134 conversion then it's easy to tell if you know what to look for because the valves have been changed. There's a multitude of dubious products to replace R12 on the market, most of them aren't any good.
    I wasn't aware that diesels sold in California had any emission controls or requirements. Shifty, do you have any comments on that?
  • gagricegagrice San DiegoPosts: 28,678
    Around $25 per 12oz can.

    I believe it was $6 for the same 12 oz. Dupont R12 in Mexico. It is all tax in the US.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,647
    Well I don't like amateurs messing around with R12, both for their safety and everyone else's. I don't know why everyone makes a big deal out of this. You just go to an authorized shop and they have plenty of R12 to sell you. I just got an R12 recharge on my Porsche, including of course leak testing and the whole bill was $100. Screwing around with cans on eBay or going to Mexico instead of sipping coffee and watching a pro do it for $100---well I don't get it. Sure, if you need actual mechanical WORK on your AC, that's expensive, but that's expensive no matter where you go. Any pro AC shop is going to charge you, and parts prices are parts prices. I have used a used compressor on one 300D, to good result, so that saved money.

    1992 300D Purchase: Well, look, if the car was in good mechanical and cosmetic condition it might be worth $6,500. So you have $4,500 worth of room here, which is pretty good.

    I'm not a big fan of "Mickey-Mousing" these cars to get them to work. The climate control issue can be diagnosed and you can get an estimate....always think "worst case scenario" a complete and utter PESSIMIST when the buyer. The seller can afford to be an optimist, you can't.

    As for the "starting problem", you weren't clear what that was about but if the mileage is very high on this car you may very well want to have a compression test or cylinder leakdown test done. Most Benz diesels don't start because of minor things like bad fuel or bad glow plugs (they do need replacement every few years) but sometimes they are just tired in the cylinder head region. Diesels rely purely on compression to ignite the fuel so if it's low the car isnt' going to start easily no matter what you do.

    AC and diesel operation have no connection that I can recall, unless you mean that if you have a leak in the vacuum lines that control some AC systems, then yes, this vacuum leak can affect engine operation. But if your vacuum lines are tight, you can just throw away your rather fussy and marginally cold 300D AC system if you wish. Climate control problems are especially bad on the W123 models, gas or diesel. A common issue is that dirty coolant (a maintenance boo-boo) jams the valve on the servo that controls coolant flow. Another common problem is the loss of vacuum to the ducting (air flaps), and of course, the electronic issues associated with a bad control head in the dash. These systems really aren't very good and you will have to deal with them time and time again, so suck it up W123 owners and be of good cheer about it.

    EMISSIONS -- yes, starting in 1985 Mercedes fitted diesels with a "trap oxidizer", which is upstream of the turbo and was meant to trap particulate matter in a ceramic shield---this particulate matter was theoretically burned off during hard acceleration. Unfortunately, the oxidizer on these cars usually either clogs and causes power loss and overheating, or worse, the mesh inside broke up and sent metal into the blades of your turbo (ouch!). The oxidizer got better for 1986 and 87 and then quit using it for obvious reasons.

    So the problem cars with the oxidizer are:

    US models: 1985 300D, 300CD, 300TD 300SD (California models, sold in western states of the USA); 1986 300SDL (again, California version) and the 1987 300D turbo, 300TD turbo and 300SDL (California AND federal versions).

    You'd be advised to avoid these models or if you are having problems with one, this is no doubt why.
  • Thanks for everyone's insight, it has been an education! Wish I had known of this site and had the luxury of time before I bought a replace 1980's Mercedes. Well I'm stuck with it now. Turns out it HAS been converted to the 134 freon, and my "shade tree" mechanic whom I adore found the leak in 2 minutes. It's really small, is in some little valve thing that is up front close to the grill work. He put almost 2 pounds of freon in it, and it might last weeks, or maybe months. When it gets low again, then he'll replace the valve thing and "drain" the system and put in new freon? Hey, I'm a woman, this is the best I understand. He fixed the AC (for the time being) and did an oil change, all for $75. REgarding the oxidizer problem and California models, is there anything I can do to prevent this, or tell if it is happening, etc? Is this another difficult and expensive item to replace? I do have the 1985 300SD, as you might recall. Thanks so much, this site is really interesting, even to a female!!!!!!!
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,647
    Symptoms of a bad oxidizer are bad fuel mileage, a drop in performance, and overheating at times.

    No there is no cure, you just keep replacing the defective part when it dies. I don't recall the replacement cost but I'd presume it is substantial given the labor involved.

    As for climate control issues, you might be sure to flush your radiator coolant.

    Other good things to do is always add a fuel additive when you fill up. Redline diesel fuel conditioner is a good product. Read the label and follow the instructions.

    Let's see....if you have a Becker radio you can throw that over a fence, it won't last long.

    But don't worry, the oxidizer could last quite a while. If you are in California that's a plus as you have fuel with a lower sulphur content.
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