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Mercedes 300D Suggestions



  • burdawgburdawg Posts: 1,524
    Even out here in dry southern California, I've never seen an old Benz without some rust somewhere.
  • Hello all, I have recently begun researching the mid 80s 300D series. I seem to be reading a lot of good things about the reliability/safety of these cars with some concerns of cost of maintenance/repairs. I am hoping someone can either point me in the direction of further researching resources or give me some ideas of specific things to watch out for. Disclaimer: I have no real experience working on cars, however learning how is one thing I am sorta looking forward to ( with some reservations about the learning curve). I have seen several listings for cars with less than 180K miles for under $3000 and many for cars with 200-260K miles under $2500. I have read that it's not unusual to be able to hit 300-450K miles with a 300D. Does anyone here think that is accurate? I live in North Carolina so don't have a ton of cold to contend with. I would be driving the car less than 5 miles one way to work each day and on weekends when I go out for errands for a few hours. One of my objectives with buying this type of car would be to get rid of my monthly car payments, but I am wondering if I go this route if I am likely to end up with never ending expensive repairs instead. Any advice for a newbie would be welcome!
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    We could talk for hours about this-- :P --- but my two cents is that with this type of car you should buy the best, cleanest, best documented car you can find and NOT buy a "fixer-upper". There is no upside to a fixer-upper because the values are low and they aren't going to get much better except for the cleanest and best cars.

    Any car on earth can go 400K miles, even a Yugo. All you have to do is keep pouring money into it. I think you will find that any old 300D with 400K has a lot of investment in it.

    What is remarkable about them is their build quality. Where most cars literally fall apart at 400K, a 300D can still look good, not rattle and not shred its interior. But that doesn't mean they don't break down mechanically or wear out just like any other car.

    Your average taxi cab can run as long as a Benz but it won't look at good, is my point.

    As for things to look out for:

    NEGLECT -- greasy oily engine, rusted body, dents, mildew, balding tires, filthy trunk, broken lenses, etc. Stay away from cars like this

    ENGINE -- many 300D engines are tired. Look for danger signs such as lots of oil in the air filter (blow-by) and hard starting when cold. A 300D engine should a) start up quickly and b) peg the oil pressure gauge when cold---that oil needle should literally click as it hits the highest number and the needle stop

    NOISE-- a rattly engine, noisier than usual (they aren't very quiet normally) could mean bad injectors.

    SMOKE -- 300Ds smoke a bit on acceleration but it should NOT be clouds of noxious smoke. This could be bad injectors or bad injection pump timing.

    HEAT/AC --- notoriously unreliable controls. check for ALL functions before you buy.

    CRUISE CONTROL -- notoriously unreliable. Almost always a bad amplifier located behind the console. About $100 to rebuild + labor.

    REAR SUSPENSION -- sagging back end, front end up in the air? You have a failed hydro-pneumatic compensator. Fairly big bucks.

    CLUNKING ON TURNS? -- bad CV joints in the rear axles

    HARD SHIFTING -- hard shifting is normal. Buy a neck brace, you'll need it. But LATE shifting could mean a vacuum leak or bad vacuum modulator

    DOOR LOCKS -- these are vacuum operated by little motors in the door panels. They often get slow. The motors are rebuildable and don't cost too much.

    BEST CAR TO BUY? --- Definitely choose the TURBO models. Do not pay extra for the coupe, they aren't worth more and they are less practical.


    always use fuel conditioner every fill up
    use anti-gel for the fuel in cold weather
    change your fuel filters (two of them) FREQUENTLY
    make sure the valves have been adjusted at least once in the last 30K miles
    change the oil every 3,000 miles come hell or high water

    FUEL MILEAGE -- you will hear all sorts of silly claims but in fact you will get about 18-22 mpg city driving and about 22-26 highway driving

    TOP SPEED -- diesels this old don't like to rev. 75--80 mph MAX is more than enough for this car. Drive faster and you'll crack the cylinder head sooner or later.

    PARTS-- lots of stuff on the Internet, and the MB dealer still carries an amazing number of parts for this car

    REPAIR MANUALS -- you can't beat the 3-volume factory manuals, but you'll pay over $300 for them.

    SPECIAL REPAIRS -- you cannot work on the fuel injection pump. This goes to a specialist and costs about $1,500 to repair. They are very rugged and should be fine if nobody messes with them.

    Good hunting!

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  • texasestexases Posts: 7,728
    The only other thing I might recommend is to check out a low miles/big $$ 300DD so you'll know what a good one is like. This way you can discount the 'they all do that' line from someone trying to sell you a junker.
  • fintailfintail Posts: 41,610
    That reminds me, the other day I got behind a powder blue early 80s 300CD turbo coupe in very nice condition...on a highway on ramp. I prepared for the worst, but the car barely smoked upon acceleration, and it was up to 60mph like any other car. It was refreshing to see one like that.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    It's all about clean fuel, replacing the injectors every 100K miles, and having the injection pump timed by an expert. So few 300D owners do this.

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  • i will agree, as i have an 87 diesel you begin to introduce turbo boost, you need to have more fuel introduced to accomodate the larger volume of air. you have a fuel pressure regulator that is positive manifold pressure controlled. as the boost increases with rpms, you will only see this extra fuel if your vacuum line out of the manifold is good. check this vacuum line(it leads to the top of the fuel injection pump). if this is cracked you will have 3 problems. minimal boost due to low fuel. minimal power due to no boost. and the transmission will not shift correctly because you are giving a large throttle input which leads the transmission to believe that you are in a heavy acceleration.

    if it isn't a bad line, i would suggest that your fuel heater loop, which may not exist on earlier models could be introducing air through a bad o-ring.. i eliminated this fuel heat loop, which simply keeps a small amount of fuel warm when the block heater is utilized. it has a small fuel jacket that runs a small around of fuel into the block, it's really not necessary unless it gets well below 0, even then i've not had any difficulty in cold weather with out it!!

    hope this helps

    aircraft maint
    fix everything else that breaks tech
  • Hi, I have a question. I changed the oil on my car and didn't tighten the lid on the oil filter. As a result I lost all my oil and the car died. When I refilled it, it started again but was not shifting normally and started overheating. Now I hear some kind of a knocking noise, it won't start and if it does, it does not stay on. My local mechanic told me to unplug the battery and touch the terminals together to reset the computer as well as try to degrease the oil around the spill part. I did both, but it seem to not do any good. Any suggestions on what I ought to do, and how much I should expect to spend on this?
  • burdawgburdawg Posts: 1,524
    You probably have a big problem. If it ran without oil until it died that knocking you hear is most likely a bad bearing (probably a rod journal), and with overheating and not being able to run for any length of time it sounds like the engine is fried. I'm not an expert on diesels, but the bottom end (rotating assembly) in a diesel is under a tremendous load with the compression that it develops. It won't last long without oil pressure.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    Sounds to me like the engine is toast. That's too bad. I'm sorry :cry:

    Your car doesn't even have a computerized engine management system. That was weird advice for an '84 300TD.....oh well.....

    I guess to be sure you can have it towed to a Mercedes diesel specialist and pay the diagnostic fees. We aren't with you so we can't hear what you're hearing. If the engine is ruined, I think you just have to let the car go or buy another one just like it.

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  • I've read many of the posts. Have found many to be enlightening. However, there are a few (actually more than a few) things I'm not clear on.

    (1) Redline products are mentioned quite often as having the best fuel additives but rarely, if ever, is a specific one mentioned. For example, there is RL Anti-Gel, Redline 85 Plus, etc. Of the many Redline products, which is the best or most recommended for use in a 1985 Turbo.

    (2) Many come in a winterized version. How do I identify it?

    (3) What is "pour point"?

    After reading the posts I'm certain that I need fuel additives. I just don't know which one(s).

    I live in Massachusetts where so far most nights have been below 20 degrees F. Daily temperatures may reach 45 degrees but are usually at the freezing mark.

    I have a block heater but I'm not sure it works. Most mornings it will not start. When the temperature rises to 45-50 degrees it does. Unfortunately, it sits in my driveway and for the past two weeks we have had a lot of snow.

    I'm new to diesel automobiles and I need a lot of help.

  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    The Redline product for diesels says "diesel conditioner" right on the label. This is not always the same as "anti-gel", which is for very cold weather.

    Also you have to change glow plugs every few years, just like spark plugs, or you won't start up very well in cold weather.

    The block heater is an excellent idea for you and you should investigate how to get it operative. I presume this is a WATER heater, not an oil heater. But if it doesn't work, just keep the battery warm with an electric heating pad isn't a bad idea, or putting a shop light under the engine to warm it up a bit.

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  • rcastorcasto Posts: 4
    I bought a 1985 mercedes 300td not running. The previous owner said he was driving and it just died. It has 240,000 miles.When i try to start it the glow plug light comes on and goes right out.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    One or more bad glow plugs would be my guess. Change 'em out. Easy and cheap.

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  • zadamszadams Posts: 11
    you may have to get some more specific information out here. If the car "died" while it was being driven, then it stalled out becuase the engine was not combusting fuel. This either means that there is an air or fuel delivery problem to the combustion chamber, most likely fuel. A car that old could have bad or clogged injectors, a bad injector pump, a bad lift pump, etc. There are ways to isolate which.

    Also, sometimes glow plugs can come up to temperature quickly (8 seconds), so you need to be more specific than "right out". Depending on your climate and season, the glow plugs may come up to temp fast and not need to be on for long. If you are trying to start the car at 60 F or higher, it should start without the plugs, FYI. Let us know...

    1985 300td
    195,000 miles
    WVO converted
    10,000 miles
  • lydia2lydia2 Posts: 18
    1. Try plugging it in to get the battery, etc. charged up. Do the windows/doors lock and unlock ? Lots of stuff drains these cars and if the temps outside are cold, plugging it in is mandatory to keep everything working. Check the alternator and bushings if batteries keep failing to keep enough charge.

    2. If the battery and glow plugs are good, Is the ignition gone? I put in a generic one after using the screwdriver for a bit, when I took out the old one!

    3. When my 1983 almost stopped (max speed was 20 km) while I was driving, it was a totally dirty transmission filter, which should be changed occasionally. After sitting all night, enough drained through to start it in the am, but soon after same thing happened. The mechanic topped up my filter!!Not good, had to change it.

    4. Good luck! These are good cars.
  • rcastorcasto Posts: 4
    I checked it out. It was the timing chain. When turning it over, the cam doesn't turn. You can take a screwdriver and move the timing chain back and forth.Not having it apart I don't know if its broke or stretched.
  • burdawgburdawg Posts: 1,524
    If the chain is still on the cam gear then I doubt it's broken. It could be many things - chain is stretched past the point of the tensioner range, broken woodruff key on the crank gear, bad crank gear, broken crankshaft (does the harmonic balancer/pulley turn when the engine is turned?), many others I'm sure. The only way to know for sure is to pull the front cover and look.
  • rcastorcasto Posts: 4
    I took the top cover off. Pulled on the timing chain and about half of it came out. It has broke. It wouldn't pull out of the engine.Also plastic that looks like part of the slider rail came with it.
  • I have been looking for a good shop manual for a 1990 2.5L turbo
    If anybody has any suggestions on what type and best place to buy it let me know
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    The dealer has the best manuals, but they are $$$.

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  • texasestexases Posts: 7,728
    Knowing nothing about these engines - are they 'interference' engines? It just seems that with the super-high diesel compression ratios that a broken timing chain could result in big problems.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    I"m amazed that timing chain wasn't rattling like the bats of hell before it broke. But then, on a 300D, how could you tell? :P

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  • rcastorcasto Posts: 4
    I forgot to post, the first three cam towers are broke. Can I run a compressin check to see if the valves are bent? also are the cam towers replaceable? Can I put a timing chain and guide rails on without pulling the engine? sorry for all the questions, I am new to Mercedes.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    I don't think it's an interference engine. I'd say your best bet is to buy a sound used head and have it rebuilt. That way, all the parts in there have been running against each other for years. If you put on new rockers over an old camshaft, not a great idea. And yes, you should be able to replace the chain, guides and sprockets without pulling the engine, presuming you haven't had damage to the crankshaft nose.

    You'll probably want the factory engine manual if you are going to tackle all this, and of course, a good machine shop to rebuild the used head.

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  • burdawgburdawg Posts: 1,524
    I wonder if the cam towers broke and caused the timing chain to break, or if the chain bound up and broke the cam towers....
    Sounds to me like your best bet is to find a good low-mileage engine, which isn't a small task for this age of car. With 240K I'm not sure it's worth rebuilding this engine, especially with possibly catastrophic damage lurking somewhere else.
    I'm not an expert on diesels, is the cam tower casting a seperate part from the head like on the old straight six gas engine?
  • ghoffmanghoffman Posts: 3
    I am a "newbie" to MB, Just bought this pristine 93 from the original owner I have all service &maint, records from MB dealer so I beleive the 97,000 mi.I probably payed too much 5,000$ but , "ya gotta love this car" as I am a big guy ,6'3" 350# and this is a car I "don't have to wear" I will be replacing my front ball joints asap as the squeeking is not very MB like.Any sugestions would be appreciated
  • burdawgburdawg Posts: 1,524
    A ball joint squeeking? That's a new one on me, but I suppose it's possible. Isn't it more likely a rubber bushing though?
  • texasestexases Posts: 7,728
    Now that I found a photo 300D long block it's hard for me to imagine other than 1) timing chain breaks 2) immensely strong diesel piston rams open valves 3) Cam towers break as valves push up on camshaft.

    Unless the owner is rich and a masochist, this engine would seem to be toast. You might as well pull the head and see what happened to the pistons. Might there be a small possibility that a replacement head would do it??
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 57,330
    I think the head was worked on previously and not done very correctly.

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