300SD Questions

[Bruce Bonds]

I'm looking at an '84 300SD. The ad says "New top end / transmission, app. 150K." Does this mean that the engine has been partially rebuilt and that the transmission has been replaced? Also, what are some other "high cost repairs" that I should look for in this car. The odometer says 147238.

[RG5384]

top end rebuild could mean nothing more than a new head gasket, or it could mean new valves/seals, springs, timeing chain etc. The best way to find that answer out is to ask. Also, with the transmission, check to see who did the rebuild, was it some "low cost transmission" shop or a reputable MB specialist? what is the overal condition of the car? those two things on a car with only 150k kind of sends a red flag up IMO, my 83 300SD has the original top end/all engine parts and original tranny, and it was fairly neglected after about 80k. The a/c can be costly to repair, as can the sunroof if you dont know how to do it yourself. My sunroof cost around 400 to fix even with doing almost all the work myself. However, it hadn't been opened in over 7-8 years(was sealed shut by respray etc..) Make sure you have the car checked for compression and overal inspection done. Front end work can also get costly, however most the parts are cheap(rubber bushings etc, labor kills you if your not a DIY'er) A quick check i would do with the engine is, after it is warmed up and running, open the oil filler plug and check to see how much smoke/oil is coming out. Alot of oil/smoke means that it has a blowbye problem, and that the top end rebuild was probably done shotty. If all checks out these are great cars and will run forever, but unless you want a thin pocket book you have to do alot of the work yourself. not trying to scare you off at all, they truely are great/reliable/unique/great-riding cars, and the quality of the materials used is unparralelled to any newer car. Good luck and let us know what you find out!
Ryan

[JimSmith]

Bruce Bonds,

There are lots of threads with the same question for nearly every car Mercedes made. In general the items you need to be aware of are not necessarily Diesel related items. The basic car you are looking at is bulletproof if the machine gets the simple oil change and valve adjustments per the maintenance schedules, meaning 3K miles to 5kmiles for oil changes, 15k miles for valve adjustments, and an annual set of fuel and air filters.

If the head has been off at that mileage I would suspect someone did not adjust the valves regularly. As they work the valves pound their way out of the head, which will tighten up the clearances until an exhaust valve burns. Also, it may be an indication the previous owner overheated it, which can also damage the head.

I am not a fan of automatics, and until MB forced me to buy a car with an automatic about ten years ago had never owned one. I still have not meddled with one so I can only parrot what others have noted on the forum. You might be better off to do a search so you get things in context. But the transmissions seem to be pretty robust, not the same as the engines, but pretty good. Several hundred thousand miles seems to be a reasonable life expectancy. The fact that the car you are looking at has a new one at 180K miles is probably good, as you should not need another for quite a while.

Other things to look for are the Automatic Climate Control (ACC) system. A very complicated system that runs on electrical andvacuum controls. The actual thermal cycle is pretty standard, with equipment from just about every automotive airconditioning manufacturer available. But the controls, push button panel on the dash that activates vacuum actuators for valves and flaps to control flow paths, is complex and full of parts that are subject to failure modes based on time in existence. And your candidate car's age is getting pretty close to when things can start failing. Lots of help on the forum though, as many people have tackled this successfully and posted instructions and pictures.

The vacuum system is used for a few other things, like locking and unlocking the doors and trunk and gas filler flap, and shutting off the fuel to the engine when you turn the key to the off position. Another set of parts that develop small cracks and leaks that can be perplexing to understand without help. Again, lots of help on the forum on these questions.

I would have a compression test done on the engine to make sure the head repair was done correctly and solved the problem. Also, when the car is running, lift the hood and remove the oil fill cap to check for blow by. You will see a substantial amount, but if the oil fill cap is hard to put back on you have a tired engine. The engine should be easy to start, the glow plug light should run for ten to twenty seconds, depending on your local temps. It is normal to puff a little when it starts up, but withing twenty seconds or so the idle should be an even, perfectly timed mechanical orchestra. Lots of activity, all audible, but all in nearly perfect timing. As time goes on these sounds become comforting as you learn they are sounds only a really well running machine makes.

While you have the hood up, look around for coolant leaks, oil leaks and Diesel leaks. Oil and Diesel leaks are pretty normal maintenance issues, while coolant leaks are probably more serious. Left unattended they can result in overheating and other further problems. Typical coolant leakages areas will be the water pump and the hose connections. I have never had an original MB hose fail. But they do or can leak at mechanical joints.

Well, that is about it. TXBill, if you see this making a list of these questions might be a good topic for the FAQ. I have never checked, so maybe it already is there. Hope this helps in your decision making, and good luck, Jim