I qualify my question by saying that I’ve reviewed the tons of great information about the infamous OM603 head cracking. However, after reviewing the material, and material about the A/C compressor clutch, I’m stumped as to the cause of what is happening with my car.

The starting event was that the rubber for the A/C compressor clutch tore. Fortunately, this was not a clutch seizure. My A/C guy suggested it was likely due to high engine temperatures, caused by a failing viscous fan clutch and weak electric fan. The fan clutch did have the tell-tale dirt and grease and the blower was weak, so I replaced both with Behr and Bosch parts respectively.

About a month later, after replacing the parts, the clutch tore again. My A/C guy was able to get a replacement, with no charge to me. He also verified the compressor (which is a 2 year old rebuilt Nippodenso) worked correctly and there was no obvious problem with the system. If this happens again, he wants to put in a new compressor, which is logical. However, it doesn’t compute to either of us and before I go that route, I want to make sure I’ve covered other bases before going to the expense of buying a new compressor, just to have the problem repeat.

I suspect a cracked head may be causing higher engine temperatures, melting the rubber in the compressor clutch. Here are my symptoms.

• High engine temperature, especially at idle. 100-105 plus degrees (prior to this summer, it never exceeded 95 at idle). It does go to the expected 85 at speed.

• After running the engine, I open the hood (with it running) and feel a blast of VERY hot air coming from the right side of the engine fan, between the block and the radiator. Coincidentally, it’s near the compressor. Of course, the engine puts out heat, but I don’t remember it being hot enough to nearly singe my eyebrows!

• Original (#14) head. Trap Oxidizer replaced at some point prior to my purchase in 2003.

• Hard upper radiator hose after overnight cool-down. Opening the overflow releases pressure and the hose becomes pliant. Textbook, I know, BUT …

• NO coolant loss noted in two years. The Coolant Idiot Light comes on sporadically and the level does go down at higher RPM. I checked the sensor for resistance – it checked OK.

• NO white smoke from acceleration.

• NO oil mixed with coolant visible. No foam on top that I can see.

• The electric fan works, at least at idle with elevated engine temps. The viscous fan clutch appears to be working correctly.

• The Behr radiator is of recent vintage since it has the reinforced neck.

Cutting to the chase. Do the mixed symptoms indicate a cracked head? If so, how long do I have to save $$ to replace it? Unfortunately, none of the threads I reviewed give a timeline, or the severity of symptoms. BTW, I am very clear on what must be done in the case of the head replacement and I will not cut corners, should that be required. I just need to know if my suspicions about the cracked head are correct, or if I should investigate elsewhere (i.e. a new radiator, etc).

Thank you for you help

__________________
Casey Cooper
"From a long line of Mercedes ownership"

'86 300SDL 250K miles (Gone, but not forgotten); best diesel I have ever driven, too bad about the Achilles heel.

'81 240D 370K miles (Sold to my brother after 9 years and 150K miles of reliable driving!)

[Five other Mercedes in family clipped for less length.]