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*