[western]

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
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.

 

[jdc1244]

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.

 

[western]

Thanks for the quick reply and the info. I have a few more questions:
What signs signal a warp head? Do I have to open up the engine?

What should the compression be on these engines?

So a sound similar to a nail being hammered in the block should make me walk…got it, thanks!

With the car on the lift I am looking for rust and checking out the exhaust, any thing else I need to be aware of while the car is on the lift?

As for the oil pressure where should the needle be while under hard acceleration, idle?

I think there are service records I will ask tomorrow; I know it is a two owner car.

Thanks again!!!

 

[MS Fowler]

re: Oil pressure. AFAIK, on all Mercedes diesels, the gauge should be pegged ( high) at all speeds above idle. At idle, with a hot engine, the pressure may drop to a little below "2", but return the high as soon as you give the engine any speed.
Welcome to the club!
The "diesel forum" over at Mercedesshop.com is a great place for all your diesel specific questions.

 

[jdc1244]

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.

 

[western]

Thanks for the replies. Okay I will have the mechanic check for signs of over heating. What are flex discs?

Does anyone have any pics of a trap oxidizer?

SO let me make sure I got this right. The o/p gauge should always high or at least close to high regardless of the situation, correct?

 

[jdc1244]

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.

 

[western]

THANKS A LOT!!! This forum is GREAT!!! Are they expensive to replace?

 

[jdc1244]

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.

 

[western]

Thanks again for all the information. I will be picking it up tomorrow if all is well. I will perform a test drive and have it on a lift so I can inspect it.

I was told there is a very small oil leak, he stated it is in the front of the engine he believes it is the front gasket??? Any ideas?[?]

The seats are pretty rough any suggestions to bring them back to life. There are not tears just worn from the picture (bad camera).

 

[jdc1244]

Leaks are not uncommon in the high miles diesel engines, a few drops are normal. I haven’t had to replace any seats.

 

[western]

THANKS FOR ALL OF YOUR HELP!!!! I am now a proud owner of a 1986 MB 300 SDL with 158K.

I have to get the seats in better shape but it drove the 4 hour trip home just fine...(knock on wood).

It does have rust on the rear wheel well but I checked under the undercarrige and it looked great.

Overall I am VERY HAPPY with the purchase.

I just need to get it in the MB dealer to see if the trap oxidezer has been replaced...

any other preventative maint. items I should take care of soon...

Thanks again...

 

[jdc1244]

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.

 

[western]

Thanks for the welcome and of course the info.

Where can I buy the CH-4 oil? I guess the oil filter must be acquired through Benz parts department?

I was going to have all filters, and fluids changed within a few weeks. Anything I need to be wary of?

 

[jdc1244]

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.