350 SDL general questions - PeachParts Mercedes-Benz Forum

#1 06-13-2002, 04:25 PM

I've had an '82 300 CDT now for several years and can say it's the best car I've ever owned - nothing beats that diesel purr.

Just last week I purchased an '87 350 SDL and have read both good and bad comments about the 350 engine (head warping) I'm looking for suggestions on what I can do to minimize this from occuring. Also need some help understanding some relatively recent repairs this auto has had. I bought the car with 135k, at 116k the following dealer repairs were performed: replaced rear main transmission seal, front transmission pump seal, replaced waterpump & engine belt and tensioner. Replaced leaking intake gasket and intake manifold gasket.

Performed trap oxidizer recall - replaced trap oxidizer and turbo -N/C.

I can't imagine why the turbo would need replacement at 116k, this has me scared. I also notice this vehicle has a catalytic converter which my '82 doesn't. Can anyone explain? I don't really understand all the concern over the trap oxidizer - should I be concerned or did the recall work take care of any problems associated with the trap? If not what else should I do?

Also do all parts for a 300 SDL (i.e. filters etc) work on the 350?

P.S. This is an excellent forum.......I look forward to any advise provided.

PC Dave · #2 06-13-2002, 04:57 PM

When I was looking at an '87 300SDL the issue came up, and I learned the following at the time (more experienced members please correct me). The material in the trap oxidizer gradually deteriorates over time and the fragments can be sent through the turbo, hence the occasional need for the turbo replacement. After a time, the same process begins with the replacement TO, and MB suffered through repeated replacements on a number of cars. A couple of years ago MB came up with a replacement for the whole system, the oxidation catalyst (sp?), which ostensibly solves the problem for good. You should call customer service at MBUSA; if you give them your VIN they will confirm that the OC recall has not been done to your car and authorize a replacement (they were ready to do this on the '87 I was looking at but the PO had replaced the trap oxidizer with a straight pipe, invalidating it from MBUSA perspective).

Check the following link for 350 engine issues:

http://www.mbz.org/info/complaints/350D/

#3 06-13-2002, 05:40 PM

The 3.5 motor was not made in 1987. It was made from 1991 to 1996.

If you have an 87 s-class diesel 6cyl then it is a 300SDL, 3.0L which is a great engine.

sixto · #4 06-13-2002, 08:23 PM

turbodiesel is right. If it's an 87, it's a 300SDL. If the VIN begins with WDBCB25, it's a 300SDL. If the engine number begins with 603.96, it's a 300SDL.

I haven't read much if anything about 350SDL head warping. The 350SDL can have problems with connecting rods. It's the 300SDL that has problems with the cylinder head, and it's more like cracking than warping. If you have other information, please share it with the forum.

The trap oxidizer was removed under recall because it can or did disintegrate. When it does, it sends debris into the turbo which can damage the turbo. What would concern me is not that the turbo was replaced at 116K miles, but that if the trap disntegrated and caused damage to the turbo, did it cause damage further downstream? If it's held on this long, I'm sure it's fine.

I assume your trap was removed and replaced with a plain pipe covered in shiny wrap. If there's a 6-8" cylinder on the passenger side of the engine bay, you still have a trap. If there's a 3-4" cylinder, you don't have a trap.

I haven't read anything about the cat causing problems, though I've had a recognized tech tell me the cat should be inspected or replaced every 35K miles or something like that. It's the first and last I've heard of it.

If the vacuum pump has not been replaced, plan to have it replaced before 150K miles.

Sixto
91 300SE
87 300SDL

#5 06-13-2002, 10:04 PM

One suggestion. Remove the trap oxidizer!! It causes more problems than it's worth unless you want your engine to lock up sooner or later.

#6 06-17-2002, 03:16 PM

Thanks to all that responded and helped shed some light on my situation / questions.

I checked my VIN number as 'turbodiesel' recommended and it does indeed begin with WDBCB25......also according to the MB local dealer's service records the engine number is 603.96.... They told me the engine number is stamped on the engine but I haven't been able to locate that as yet.

They also presented me with records that show the trap oxidizer was serviced at 48k and replaced at 116k (along with the turbo).

I've looked for the trap on the passenger side of the engine and do not see a 6-8" cylinder as 'sixto' suggested. That makes me feel better, however I also don't see the 3-4" cyliner either. I'm looking around the battery and coolant overflow reservoir area.....can anyone direct me any closer?

I'm just a little confused why the plate on the trunk reads 350SDL, guess someone pulled a switch. I'm waiting for the title as final verification.

Since I haven't been able to locate the engine number on the engine, is there another way to verify I have the 300 and not the 350 engine?.

Looks like the only thing better than my cars ride is the assistance MB owners are willing to provide. Thanks again....

gsxr · #7 06-17-2002, 03:42 PM

Most likely someone put the late-model (90-up) badge on your '87. The trap (or foil-wrapped straight pipe that replaces it) is directly to the left of the valve cover, vertically above the turbo & exhaust manifold (as viewed standing in front of the engine). If you're looking at the battery you're too far away.

The engine number is stamped on the block, approximately above the injection pump mounting area, on the "L" shaped part behind the head. It's probably covered in grime though and VERY hard to clean without removing something like the intake manifold or fuel filter housing.

The 86-87 OM603.96x's had issues with the head cracking, possibly due to thermal overload induced by the trap oxidizer during extended city driving. The head was redesigned 3 times (4 heads) and the head gasket 5 times (6 gaskets). The 90-up OM603.97x, the 3.5L, had the "good" redesigned head & gasket but had bottom end problems with the rods & pistons. The 3.5's had a reputation of failing and requiring either a new engine or major bottom end rebuild, both of which would be in the $5-$12k range - PLUS labor. But the heads are fine on the 3.5L. They're great for donor heads, if you can find one, to replace a cracked head on a 3.0L. :p

Photos of my 603.960 head replacement are at the URL below. My car has the trap removed, so if your exhaust manifold looks like mine, you don't have the trap. Hint: The EGR valve accordion pipe connects to the end of the trap or replacement pipe:

http://www.meimann.com/images/mercedes/head_gasket/

Regards,

#8 07-13-2002, 12:51 AM

the 3.5 heads are not a good replacement unless you buy the second versions.... do not buy a rebuilt head thay are notorius for having cracks and voids at the #1 & #4 cylinder forcing oil into the coolant jacket. If you are going to use the 3.5 head buy a new one. the rebuilts (which are cleaned up originals) were known to have problems straight from the foundry. When replacing these heads always buy from MB it is worth the redesigned head. By the way the engine # is not on the head. MB puts the head part # there and there is an engine number on the block.

psfred · #9 07-14-2002, 01:49 PM

I think MB designed and installed the trap oxidizer mainly as a stop-gap measure so they could continue selling diesels in California in 85-87. It was known to require extra maintenance and was also known to probably not be a final solution to excessive soot generation with the the current diesel designs -- probably when the 603 isn't in current production as there isn't anything seriously bad about the design. The newer CDI/TDI engines make less soot and more power.

When the trap goes bad, it sends chunks of creamic material through the turbo, killing it. MB always planned on replacing the system if it failed, since California requires lifetime emissions control, so when the catalyst was worked out, they changed over. There is a performance boost as well, and there is no restriction on the use of additives. The catalyst will not harm the turbo. Replacing it with a straight pipe will do essentially nothing for performance, and will void the warrenty on the turbo, it any.

The head design problems have been solved, but the aluminum head will still crack if severely overheated. One is well advised to use only MB orange coolant and to keep an eye in the upper radiator tank nipple, expecially on Behr rads - it gets brittle, particularly if green coolant is used (the anti-corrosion compounds are different and affect the plastic). If the nipple breaks off at speed, you will fry the head pronto. Not good! You should also watch for oil in the coolant tank, indicating a leaking head gasket. Head gaskets will fail more frequently with the aluminum head than with a cast iron one -- roughy every 150,000 miles.

The bent rod problem is sporadic, if fatal to the engine. The 3 L suffers from bent rods, too, usually #1 or #6, but not like the 350. The rebuilds are fine -- the rods are about 3 or 4 oz heavier! Rebuild will require all new rods, sleeves, and new pistons -- about $5000 in parts. Used good condition engines are just about non-existant.

My advice is to keep the thing in tip-top shape, do the maintenance religiously, and don't worry.

Both of ours run like a dream, 174,000 on one (new head) and 130,000 on the other (had trap oxidizer changed last fall!)

Peter

stephenson · #10 07-14-2002, 04:50 PM

Dave M.

Thank you for putting the photos on your site - that is so cool! Being able to actually see the parts in disassembly and assembly is absolutely great!

Keep posting them ... they are a life saver.