Need Help: Head Gaskets Leaking


Apr 1, 2011
1990 Mustang GT pretty much stock other than 7lb. Kenne Bell supercharger kit.

I'll try to give the short version. Engine has been running lean (Code 91) and richening mixture. Found a couple of cylinders leaking into cooling system with 100 psi on cylinder. Pulled heads had them resurfaced (.007" removed)and installed Fel-Pro performance gaskets with ARP studs. Put it all back together and the same problems reared their head. Code 91 and later found leaking into cooling system with 100 psi pressure put on cylinder. Took whole engine out and went to the machine shop. Machinist started checking things. Heads were already resurfaced but will pressure check them and the block. Did notice a bit of coolant migration on engine deck near top. Then he measured the combustion ring on the head gasket that had about two hours on it. He "mic" ed it and noticed that that on all cylinders, the combustion ring ring was compressed about .002" more on the exhaust side of each deck as compared to the intake side of the combustion ring on all cylinders. He summized that the head was not totally sealing and compressing the combustion ring uniformly. this was resulting in coolant leaking slightly and one combustion ring showed a darkness indicating a leak past the combustion ring on at least one cylinder and the surface composite material looked wavy like it was being pushed away from the combustion ring (failure). He suggested that I contact ARP and question them regarding their torque specification of 80 ft-lbs. for the head bolts. I told him "you know they aren't going to admit to anything". Anyway, I called them and they didn't admit to anything. They stated that the intake bolts being longer does not affect their clamping load whether they are long or short. So, why after addressing the problem with new gaskets, studs and shaving the head am I experiencing this problem. I am aware that some guys torque the intake side head bolts to 5-10 ft-lbs. higher than the exhaust but I cannot believe this then seals it all up ... or even going back and retorqing the head. The gaskets were Fel-Pro Performance Permatorque gaskets that do not require retorqueing. So what gives here?? The Machinist also measured block and did not find any major deviations except around one cylinder it was .002" - .003" low which would explain some coolant migration. But, it does not explain why all of the combustion rings are compressed .002" more on the exhaust side of the head as oppossed to the intake side of each head. I also doubt removing .007" from each head has caused the intake to lift the heads or something and my machinist didn't even mention it as a possible cause. So, why aren't my head gaskets compressing evenly ... I did everything like everyone else does when they blow a gasket ... install studs, replace the gasket and have the head resurfaced. And I only ran the motor for about 2 hours after re-installing everything to find coolant leakage again under pressure. What gives here ... not enough time for the supercharger to place any great strain on them going around the block and back and running in my garage testing things for only around 2 hours. Engine vacuum after the repair did not rise any as I thought it should ... been hanging around 14-16 in.hg. with valve job (new springs, seals, and resurfacing) etc.

Engine did overheat about 2 years ago fwiw. the lean code (code 91) was dumping a lot of fuel in and the combustion leaks dirtied the oil almost black in 2 hours of run time. While at the machine shop, the heads and block will be pressure tested and I am purchasing a forged bottom end to be balanced while in there.

So, while putting all of this money in this thing, what is causing the above conditions of leakage and differences in crush amount on the combustion ring ... no one seems to know or can give me a definitive answer especially if the pressure tests show up as okay. I just do not understand this. I have 30 years of engine experience and have troubleshooted some crazy problems over the years but I usually get the real problems. I don't want to put this back together and have the same thing happen again ... I'm supposed to be driving the car now for the Summer. Re-torqueing permatorque head gaskets or increasing the torque 5-10 ft. lbs. (not specifically recommended by ARP) just doesn't seem like the real problem that could be causing such a bad running condition with so many problems only small adjustments at best. Or, a few thousands on one cylinder deviation on the block should cause such a problem across all cylinders on both sides. The head gasket is supposed to pick up small deviations and seal them. It seems like the clamping load across the block is higher on the exhaust side of the head than the intake side due to the differences found in the crush of the combustion ring. Whatever the cause, it led to the first failure and now reared its ugly head right away ... wtf is going on here???

Any insightful help into this problem from experienced individuals would be deeply appreciated because I want to identify it, fix it, and put it to rest and enjoy my new engine and not end up in this same nightmarish situation. Thank you! Sorry so long, wanted to give all the known facts.
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