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  #1  
Old 06-11-2018, 05:54 PM
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Quote:
Originally Posted by Diseasel300 View Post
A crack in a cylinder head can most definitely allow combustion products into the cooling system, but not coolant into the cylinder.
Only if the crack is opening under combustion pressure. It is possible but not common and I've never seen on in person or discussed in a trade magazine. I'm basing this on decades of real shop experience across many makes.

The world is made up of more than friction-less pulleys and ideal gasses. ( Think about the ideal gas law for a bit, what I state is more subtle than you think. )

As for checking for a combustion to coolant leak with sub 90 PSI air, read this

M104.980 too much radiator hose pressure?

This links to a rad pressure on an aluminum head M104. Post 18 says

Quote:
A leak down test confirms it. I went in order of 1-5-3-6-2-4 and 3 was the one that was leaking into the cooling system. Pressurized the cylinder at TDC with around 30psi and I heard bubbles in the coolant reservoir.
Have a look at the pic, the fire ring on 3 is intact and only slightly dark on the drivers side. Granted we can see the underside of the gasket but gee, our guy found the leak at 30 PSI. Number 1 is at bottom.
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DIY OM603 head pressure test - head good?-cyl_gasket_3_leak.jpg  
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  #2  
Old 06-11-2018, 06:19 PM
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Coolant was getting into the cylinder in the example posted. If the hood is still present and even if not. Could you not have a look at that engines cylinders? That the used head came from?

It would not be conclusive if a cylinder was not washed down. Actually steam cleaned. At the same time if one appeared to be. You then have a solid indication of not to risk using the head.

When I mentioned can act like a one way valve. Molecular size and charactaristics of elements and materials do enter into the picture at times as well. You probably remember when synthetic oil was introduced. People were screaming about their engines leaking out. Besides any solvent type action. The base of synthetic oil was probably involved in another way. In any event the synthetic base was modified and the problem drastically reduced. You seldom hear of it anymore.

A mans repair approaches to things are his own business. No matter how sorrid or counterproductive they may be or may not be. They are his. In this case sure it may work out. Or may not. Your gamble.

I understand this. There is only one sure thing. The odds do not favor this approach. Still you could luck out and say I told you so. Personally I would like to see it work out than not. Say it even did. Would you be thinking of the cracks all the time and always waiting for something. They are not going to self heal up.

Last edited by barry12345; 06-11-2018 at 06:48 PM.
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