External coolant leak on TO30 cylinder head

CharlesT · Aug 18, 2019

Have a coolant leak on a to30 cylinder head. Engine is a newly rebuilt Z129 continental. Coolant initially shows up externally around #2 and #3 spark plugs, eventually puddles beneath the plugs a runs down the side of the block. Leak is a slow one, takes several days before it runs over the edge and down the block. Goes away when the engine runs and warms up, but always returns after a few days of not running. No signs of any coolant leaking internally. Head was checked for cracks and surfaced during the rebuild process which showed all good. Wondering if the checker missed something, etc. Has anyone else had this problem? All I can figure is a hairline crack around these 2 spark plug ports.

Steve@Advance · Aug 18, 2019

That's not a common problem to my knowledge, cracking around the plug area.

Is it possibly coming up the stud hole and under the nuts?

Maybe some sealer under the nuts. Only remove one at a time.

Did you do a retorque on the head? If not, might give that a try. Back each bolt/nut off one at a time just enough to feel it move but not relax the downforce, then take to torque spec.

Then adjust the valves.

Might try some Barsleak tablets. They work well and are non clogging.
Barsleak

CharlesT · Aug 19, 2019

Definitely not originating around head studs. Yes I have sealed and retorqued all bolts to spec., and set valve lash again to proper specs. I have also tried stop leak, can't tell that it made any difference at all. I have cleaned and dried the area numerous times in an effort to pin point exactly where the leak is coming from. The machined area where the spark plug gasket seats is where it shows up first, (appears as if it is coming from around the plug threads) then runs downward and puddles around the head bolts eventually getting enough to run over the edge and down the side of the block. Even sealed the plug threads just to see if that effected it, no change, so it isn't coming from around the plug threads. It is the strangest thing. I too have built many engines and have never seen anything like this in 40 years. Thanks for the reply and for any thoughts that may come to mind.

Steve@Advance · Aug 19, 2019

Something to try, get it up to temperature, pressure up the cooling system, just a little, maybe 5 lbs so not to damage the radiator.

Pull the 2 plugs, see if anything reveals itself. Look inside the cylinders too. Spin it through the next day, see if anything comes out.

CharlesT · Aug 19, 2019

Thanks, we are looking at a couple of other things as well.

CharlesT · Sep 3, 2019

UPDATE
Did a cooling system pressure test, found small leaks at spark plug counter bores of cylinders 2-3-4. No outward evidence of cracks, although there must be some tiny ones. Leaks were minor, so I mixed epoxy and applied it to the outer edges of the counter bores. Let it cure over night, refilled system with a 50 / 50 mix of antifreeze and water. Ran the engine until warmed up to temp, saw not leakage. Let it sit over night, all looked good the next morning. Did another pressure test to 7 PSI, no sign of leakage. I have since run it through several heating and cooling cycles and watched it closely for a week; all good at this point. The only thing I can figure is that rust on the head coolant passage interior has worked long enough to make the casting very thin in this area allowing a very small area where metal is thin enough having tiny crevices for this to have happened. This is a guess, and I will continue to monitor the situation, but for now, there is no leak, all appears well.

External coolant leak on TO30 cylinder head

CharlesT

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Steve@Advance

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CharlesT

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Steve@Advance

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CharlesT

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CharlesT

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