87 300td head questions
 

I have the above(124 chassis, so it's the 6 cylinder(I don't have all the engine series numbers fixed in my head)) with a small coolant leak. I can find no coolant leaking externally. I think the head gasket has a pinhole leak because the cooling system builds pressure pretty much instantly - like in 30 seconds you can hear air escaping when you crack the cap. No matter what the temp of the engine. My past experience with diesels and head gaskets has been with the 1.5/1.6L VW IDI diesels where it has been an all or nothing proposition - in that either it was good, or you had massive airbubblage. The engine has not been over heated on my watch - which has been about 4 months. It supposedly has 133k on, which I doubt as the odometer mostly doesn't work, but when it does it's accurate as near as I can tell. To the questions:

1)Is there anything other(IMHO a very remote possibility) than a pinhole leak that could force air into the cooling system?

2)Are there various thicknesses of headgaskets available due to piston protrusion(as on a VW 1.5/1.6 idi diesel), or the like out of the block?

3)What's a #22 head, and how can I tell? How can id the head in general?

If you coolant system is pressurizing when cold it does sound like a Headgasket or cracke head issue.

Ok, I finally got the head off. Found the cylinder that was leaking - must have been the head gasket even though the sealing surfaces only showed a couple of places that might have leaked as they weren't clean like the rest. No cracks in head on that cylinder, but two others have some cracking between the valve seats. On one cylinder the crack is just starting to form, and on the other it's (call it) 1mm wide. At what point do they usually start to leak as far as the cracks go? Neither of these cracks would be an issue(leak wise) on a 1.6L VW IDI diesel of which I have plenty experience with - I have one that had cracks bigger than this over 275k miles ago when I just put the head back on to see how long it would go and it still runs with no issues due to the cracks. So to reiterate, how big can the cracks be before they're an issue that must be addressed now? Also, what are the flatness specs for the head? Are the head bolts TTY(Tighten to Yield) and as such should be replaced every time(On removal some were much tighter than others). Also, do the head gaskets come in various thicknesses(like for the 1.6L VW diesels), or is it one thickness fits all. BTW the head is a 14.

On a side note, are there any good manuals out there? I find the Official Mercedes Manual to be rudimentary at best. I haven't been able to find all sorts of vital (engine) specifications as of yet - let alone clear instructions and illustrations on a consisten basis. Good thing I'm mechanically inclined with experience.

Thanks.