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300 sdl questions, buying it very soon, HELP!!!

1962 Views 14 Replies 3 Participants Last post by  jdc1244
Good afternoon,
I am about to buy a 1987 300 sdl. What should I look for? I am having the shop perform a compression test and a car fax. The car has about 154K on it. Is there a website dedicated just for the sdl? I have looked but most w126 websites deal with 420 or 500 with very little mention of the sdl specifically. I searched these forums but the information is general at best and I am VERY new to the diesel thing. I have also checked out the mercedessshop but they also have limited pre-buyer information for the 300 sdl, at least when I searched they did :D
How should the transmission shift, any funny noises I should be aware of when I test drive the car? Any leaks I should look for? I know about the trap oxidizer, but I have not seen a pic of what a trap oxidizer looks like and what the replacement should look like.
Any assistance you can provide would be of GREAT help.
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These engines have aluminum heads that can warp if the engine is overheated – check for that. Otherwise they are excellent engines. You don’t want excessive smoke, hard starting, overheating, heavy shaking, oil pressure should be good, and no “nailing.� If you hear a sound that sounds like a large nail being hammered into a block of oak, walk away – you’ll know it when you hear it. The transmission should be quiet and the steering track straight. Check for rust. Check the undercarriage on a lift. Are there service records? You may not find a lot of web info on the diesels because they were only imported to the US. Good luck and keep us posted.
I assume the compression s/b the same as the OM 617, somewhere in the high 200s to lower 300s psi, if memory serves. The mechanic needs to check for telltale signs of overheating; the trap oxidizer would clog and cause the engine to overheat; the T/O was recalled and fixed by MB, you REALLY should have records that this was done before buying the car, or at least asking about it of the owner. While on the lift at least check the condition of the flex discs, and axle assembly for excessive wear – check the subframe bushings, suspension and shift bushings. The o/p should peg at three bar when cold, idle and under load – it can be as low as 1.5 bar hot but should peg when the throttle is touched.
The o/p when the engine is hot can be as low as 1.5 bar. The flex discs are in the pic below – they are on each end of the prop shaft at the tranny and rear axle. The discs below are in good shape, if cracked around the bolts or if the rubber is hard (no ‘flex’) they need to be replaced.


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No, not alone – but if they’re bad a check of the other drive train parts is in order and if there are many problems, that can get expensive.
Leaks are not uncommon in the high miles diesel engines, a few drops are normal. I haven’t had to replace any seats.
Congratulations and welcome to the wonderful world of the 126! Make sure to use a CH – 4 rated diesel oil or synthetic and an OEM oil filter like Hengst or Mann. Please post questions BEFORE you do anything and don’t go to Pep Boys or Just Brakes or the like – your chain store auto repair shop days are over. Find a good MB knowledgeable indy in your area.
You need to change the oil often if using dino – every 3000 miles – if you’re having someone do all fluids and filters make sure it is an MB place using OEM filters. Try not to go to the dealer, too expensive. If you change your oil yourself Delo 400, a very good CH – 4 rated oil, can be had at Hell*Mart. The OEM filters can be gotten online from German Star, Fastlane and Rusty’s.
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