Some help please. I've come across what I would consider a fairly serious problem with which I could use some advice.

The facts are these:

1992 300D 2.5L Turbo - 602.962 engine - W124 chassis
392,000 miles
Has been rock solid since I've owned it from 332,000 miles and well maintained.

I have noticed over the past few months that it has begun to consume increasing amounts of coolant. No leaks or puddles, haven't taken notice of any excessive white smoke in the exhaust, but haven't been specifically looking for it.

In the past week, I have noticed that the normally rock-steady temperature guage has risen past normal on occaision, but nothing serious.

Checking the oil today (with the engine temperature higher than normal, but not anywhere near the red zone) I noticed a "hissing" noise under the hood. NOT at the radiator or overflow tank. The noise is coming from the hot (LH) side of the motor underneath where the exhaust manifold mounts to the head. I cannot see its point of origin, but can see some smoke (steam) coming from the area from which the sound is emanating.

I tried to limp the car home, but had to park it and leave it when the temp guage began to steadily increase until it reached the red zone. I had to drive about 4 miles until I could get to the next exit with the temperature bouncing in and out of the red zone, but remaining very, very hot.


My theories are these:

I have a blown head gasket externally that is seeping coolant onto the exhaust side and vaporizing it instantly.

Past experience with a blown head gasket tells me that the area surrounding the breach boils the coolant preventing the coolant from passing this area and ultimately overheats the engine.

I fear that the head itself has been damaged in the process.


Given all of this, I have several questions for the experts herein:

1. Do my theories sound reasonable?
2. How might I confirm these or other possibilities without dissasembling the head?
3. If I were to disassemble the head, would I readily be able to determine if the head were cracked and/or warped?
4. On a scale of 1 to 10 for a capable DIYer, where does a head gasket change fall, considering the head is in good shape.
5. What are my odds that the head is not cracked?
6. Aluminum head? Steel block?
7. If the head were cracked, could it be welded or otherwise repaired?
8. If the head were shot and I was to replace it, should I replace with new? Used? What should I expect to pay for each?
9. If I get the head off, what else ought I do to a 400k mile engine while I'm in there that will benefit me in the long run (without replacing stuff just for the sake of doing so)?
10. Any major pitfalls I need to look out for? I haven't found much in the way of procedural help on this forum.
11. Anything else I haven't thought to ask?


Sorry for the long list of questions, but I'd like to gather as much information as I can before I make a decision about whether I'm going to tackle this job.


Thanks so much in advanced for your valuable advice.

Pete

__________________
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I miss by Benz
92 300D 2.5L 403,000+ *SOLD*
87 300SDL 3.0L 252,000+ *SOLD*

While I am no expert at taking these engines apart, I do have some experience in dismantling a 617, as I am going through the exact same situation as you are experiencing.

In my case, I realized that coolant was disappearing, with no leaks, and had an oil analysis done. Once glycol shows up in the oil, the game is basically over. You need to park it soon and get to work.

So in answer to your questions:

1) Your theories are right on the money. The problem is a head gasket or a cracked head, or both.

2) You almost certainly need to remove the head at this point. I would not drive it any more in that condition. You could send in an oil sample if you are still unsure of the situation, but, based upon your description, there is little doubt.

3) No. You would need to bring the head to a competant machine shop who is familiar with these engines and can pressure test the head.

4) Changing the head gasket would rate about a 7 on a scale of 1-10. It's not for the faint of heart, but, not that difficult either, if you have the time.

5) Can't give you odds on this. Not enough experience. It can't be confirmed until you remove the head.

6) AFAIK

7) Some shops think that they can do this successfully. Some can. The question is which one do you trust? Most of us would not roll those dice.

8) Nothing wrong with a good used head. New is quite costly. Don't know the prices of that one, offhand. A typical 603 head runs anywhere from $800-$1200 used, when they can be found.

9) Well, at 400K, you might be in a situation where the engine needs more than just a valve job and head gasket. If it needs rings and the compression is low, you have to decide if it is worth putting money into this engine. Does it burn oil now? A compression test might be in order to help you make a good decision. 400K is quite a few miles.

10) You need to have the engine manual before you attempt a task of this magnitude.

11) Evaluate the overall condition of the engine, with a compression test, before spending a dime on it. You may decide to replace the engine with one from a recycling yard rather than to simply do a valve job on the existing engine. Oil consumption will also help you with this decision.

If you are going to do this work yourself, you need to have the vehicle out of service for a minumum of 30 days. Sometimes, it will take considerably more time than this.

i guess i would want to rule out other reasons such as water pump and thermostat, before moving to the conclusion of the head gasket.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Brian is correct.At 400K you need to evaluate the total engine.
Get the service C.D.s if you are going to try this yourself.
How is the transmission???
How old are the vacuum control pods inthe H.V.A.C. system?
What is the state of repair of the suspension?
What is the state of repair of the driveline?



#36B How is the exhaust?

well, good chance that the head is not cracked. and as far as doing the whole engine, the bottom end is usually the most durable part. while the head is off you should prob do the cam chain, and giudes. also the valves are suspect and the guides and the springs.

on my 90 350 sdl we had to do all of the above. the head was not cracked or unduly warped. it was surfaced but not much.

by all means do a compression test first. they also can do some pressure testing with the head on the car, i believe.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I guess as part of the decision process, I should consider a possible sale of the vehicle, so I'd like to ask if anybody would be interested in buying it.

Specs as follows:

1992 300D 2.5 L turbo W124
Light gold (desert gold, I believe) with tan leather
Runs excellent, despite the above included issue.
393,000 miles.
Transmisssion runs great
AC blows ice cold.
Everything works as far as I can think of right now except:
Tires 50%
Due for an alignment
Front right hub slightly bent, its replacement is on its way via Fedex today and will be on shortly.
A couple of very small rust spots on the back the trunklid and again on the left rear fender well.
Left rear window motor disconnected because the track guide piece needs to be replaced (about $7 and a couple hours at the most)

No pictures to post today, they're on my 'puter at work - I need to go to a funeral today, back in the office tomorrow and could post or email some then.

Located in Holly MI (48442) - just south of Flint, MI. Would assist or provide shipping, if necessary.

Make me an offer.

Pete

__________________
*******************
I miss by Benz
92 300D 2.5L 403,000+ *SOLD*
87 300SDL 3.0L 252,000+ *SOLD*