GregMN's 1991 W126 350SDL Has A New Home - Page 5 - PeachParts Mercedes-Benz Forum

Squiggle Dog · #1 09-07-2019, 10:48 PM

The engine isn't idling well. It acts like it has dead cylinders and is going to break the mounts. It still runs a bit rough even at high RPMs. It smooths out after it warms up. But, it's over 110F outside, so I don't think it's a glow plug issue. The fuel filters haven't been replaced in a while, so hopefully there will be improvement after they are changed out.

I didn't see any signs of a bad head gasket. The injectors weren't rebuilt long ago, and the injection pump is a low-mile replacement with new O-rings. Maybe the timing chain has stretched.

83w126 · #2 09-08-2019, 01:37 AM

Can't you still get the coolant tank from the dealer? I asked recently and they said there were still tons of them in stock but maybe they were wrong.

vwnate1 · #3 09-08-2019, 02:00 AM

I often find The M-B Classic Center can get me parts my lazy @$$ed local $tealer says are N.L.A. ~ shame on them, kudos to Tom and the rest of the enthusiastic and hard working people at the Classic Center .

Squiggle Dog · #4 09-08-2019, 03:41 AM

Quote:

Originally Posted by 83w126

Can't you still get the coolant tank from the dealer? I asked recently and they said there were still tons of them in stock but maybe they were wrong.

They are still available new, but they are $200.

oldsinner111 · #5 09-08-2019, 05:57 AM

is washing soda borax?

Squiggle Dog · #6 09-08-2019, 02:55 PM

Quote:

Originally Posted by oldsinner111

is washing soda borax?

While it can be used as a detergent booster like washing soda, borax is different. I believe borax is acidic, so it would not neutralize traces of oxalic acid.

Edit: Apparently borax can be used to neutralize acid. So, I guess I don't know, but it is of a different chemical composition than washing soda (sodium borate rather than sodium carbonate).

Squiggle Dog · #7 09-08-2019, 09:16 PM

I think the car has a bad engine or a cracked head. It sounds like it's about to throw a rod and won't idle right. Just about everything external to the engine has been gone through. So, I'm going to have do a compression test or somehow figure out what's wrong with it. It acts like some of the cylinders aren't firing.

It seems that I can never keep this car on the road for very long, and every time I fix one thing, something else stops working. It's become a real money pit, but a car payment on a new car isn't cheap, either.

We ordered in new heat shields, injector line clips, a gasket for the intake manifold crossover pipe, and a valve cover gasket so I can check the compression again and also see if the timing chain has stretched.

I replaced the fuel filters today and the injectors were rebuilt with Monark nozzles only four years ago, at which time I installed a low-mileage injection pump and lift pump with new O-rings. But, I guess I'll have the injectors tested. I'd take the injection pump in for testing, but they'll probably take it apart, tell me it's bad, and charge me $100 like they did when I took in the original injection pump for free testing. One thing I noticed when I bled the injection lines was that the first two injectors didn't seem like they were getting fuel.

I also have to figure out why this car is SO SLOW.

Squiggle Dog · #8 09-08-2019, 10:25 PM

I did some research, and I'm speculating the engine has a cracked head. It has a #14 head on it (engine is from a 1987 W124 300D with about 305,000 miles), which is apparently the earliest version head and is prone to cracking. The engine has had a bit of a stumble when cold, but after the car lost its coolant and fan and overheated, the stumble has been awful. It seems like the engine is going to launch itself off of the mounts.

Before the overheating incident, the engine temperature would fluctuate from normal to nearly overheating at random times. The radiator hoses and expansion tank hold a lot of pressure hours after the engine was last run. When I release pressure off of the expansion tank cap and open it, smoke comes out of the tank, but there are no bubbles or oil contamination that I can see. I also see no signs of coolant in the oil.

Hopefully I can gain a diagnosis from a compression test, or a leak-down test (which I have never before performed). Also, should the engine be able to be run without the cap on the expansion tank? I tried it and coolant immediately overflowed and spilled out as soon as I started the engine.

Update: I'm also seeing white smoke out the exhaust.

Diseasel300 · #9 09-08-2019, 10:45 PM

Head gasket is blown most likely. You may have a cracked head, you won't know until you pull it.

83w126 · #10 09-09-2019, 11:12 PM

If it is cracked I have an extra #18 head I would sell if you can figure out shipping.

Squiggle Dog · #11 09-10-2019, 12:20 AM

Quote:

Originally Posted by 83w126

If it is cracked I have an extra #18 head I would sell if you can figure out shipping.

Thank you!

barry12345 · #12 09-11-2019, 09:09 PM

Before pulling the head if possible do a compression check. Just to get some ideal of what condition the good cylinders are in. I would go for an early baseline. Add a small amount of fluid to see if the compression rises if it is substandard. Leak down test would not hurt.

You can probably find a complete better 603 engine with an updated head for about the same money or less than an updated head. Plus you can sell one or other of the injection pumps at least.

Complete cars off the road for collision or rust seem to be the best sources. Plus you can scavenge it for other parts or sell them. Depending on the area you reside in. As you know showing 305K on the odometer means little in reality with these cars.

Squiggle Dog · #13 09-11-2019, 11:07 PM

Quote:

Originally Posted by barry12345

Before pulling the head if possible do a compression check. Just to get some ideal of what condition the good cylinders are in. I would go for an early baseline. Add a small amount of fluid to see if the compression rises if it is substandard. Leak down test would not hurt.

You can probably find a complete better 603 engine with an updated head for about the same money or less than an updated head. Plus you can sell one or other of the injection pumps at least.

Complete cars off the road for collision or rust seem to be the best sources. Plus you can scavenge it for other parts or sell them. Depending on the area you reside in. As you know showing 305K on the odometer means little in reality with these cars.

Good advice. The compression numbers five years ago were: #1 405, #2 395, #3 375, #4 375, #5 405, #6 375. When I did a "wet" compression test, the numbers went from: #1 405 to 420, #2 395 to 410, #3 375 to 405, #4 375 to 415, #5 405 to 415, and #6 375 to 395. The factory service manual states healthy compression as between 377-464 PSI. The minimum acceptable compression is listed as 261 PSI, which is well below the numbers seen. The cylinders also shouldn't have more than 44 PSI difference. There was only a 30 PSI difference at most. With a blown head gasket or a cracked head, I would expect much lower compression now on some of the cylinders.

We're on a super tight budget for this job; maybe $200 tops, and the head gasket kit is half that. So, I'm really hoping the head isn't cracked because so much money has already been spent on the radiator and cooling system parts, and there is no Plan B. Every time I get this car running, it punches my roommate in the wallet and the money just isn't there.

By the way, OM603 engines are practically non-existent in Arizona. They never seem to show up in wrecking yards or on Craigslist--it's always that dang 300SE inline 6 cylinder gas engine. People in the desert must not have liked diesels.

ROLLGUY · #14 09-11-2019, 11:16 PM

I have a complete 603 for sale if you end up needing it. Not sure what head is on it, but I will check......Rich

Actros617 · #15 10-30-2019, 04:16 PM

This is a gold mine, your doing god's work with your documentation!

I'm curious in how you get your injector timing again, I'm in the same process of swapping cylinder heads (mine had multiple cracks and erosions everywhere!) with a new cylinder head from Mercedes benz (pretty steep price even after discount

) since it's near impossible to find a good used OM603.971 head's (aka 3.5L engine). I did tons of marking before removing the tensioner and sprocket but I suspect timing is off since the IP locking tool did not lock in place at 14 ATDC (per manual for MY 91+) I tried 15 ATDC and it was kind off (didn't lock), however this engine will get a new timing chain rolled in when before installing the head.