Coolant overflow

Posted by Owen_Dyneto On 2008/9/30 12:05:44

Here's a truly frustrating technical problem so let's see what hypotheses our skilled mechanics can come up with to explain it. I think you can assume that at least one observation or test must be faulty, otherwise there'd be no problem. The car in question is a very low mileage 1954 Cavalier, 327 engine with 4/bbl of course. Prior history includes a valve job, and the cylinder head was resurfaced so the compression ratio is a bit higher than stock. The problem did not arise with this work, but several years and miles later and not connected to any known maintenance or repairs.

The problem manifests itself as throwing coolant out of the overflow. At worst at Interstate speeds, it can be as much as a quart every 15-20 miles. Yes, the head gasket has been replaced (several times). Yes, it does it with several cylinder heads, all of which have been tanked, magnafluxed, checked for straightness and surface ground if required. Yes, the head was properly torqued and retorqued each time it was removed. Yes, the studs have been checked and are not stretching. Yes, it does it with or without a thermostat present. Yes, the radiator has been removed, boiled, checked, and has a gravity flow rate at least equal to the original specification. It has done this with a variety of radiator caps and the neck seat and cap gaskets seem perfect. Compression values are normal enough and quite even, though #1 cylinder is the highest. No, the water pump has not been rebuilt but is silent and does not leak. Never any evidence of coolant in the crankcase.

Now the latest information: Putting each cylinder on TDC on compression and pressurizing the combustion chamber shows no leakdown except for #1 cylinder, which has been examined scrupulously under magnification and with intense light by at least half-dozen mechanics and there is absolutely no evidence of a crack. Although the leakdown was with the piston at TDC, we have also examined the cylinder walls and again, no evidence of a crack. And remember, the several heads were checked and are OK.

Now here's the last teaser: when pressurizing #1 cylinder while at TDC on compression, the coolant level rises in the radiator (cap off) and ultimately reaches the overflow, but no air bubbles are actually seen (perhaps didn't wait long enough). BUT maintaining the pressure on the cylinder and spraying oil on the head studs and nuts, bubbling of air escaping at random studs at the threaded end as far back as #6 cylinder was observed.