Frank, what do you think the max pressure is in the cylinders with the
engine running? 1,000s of psi maybe? Cycling from near zero to 1,000s of
psi and back 10 times a second at idle. Putting a 120 psi air hose to
each cylinder will not duplicate this.

Here is a suggestion. Put a pressure gauge on the cooling system and
verify that the pressure is still going up very fast when the engine is
running at idle after full warmup. If it is, shut off the engine and
relieve the pressure. Then remove one sparkplug wire, ground it, and
start the engine. If the pressure builds again, shut down, relieve the
pressure and move to another plug wire. When you get the one with the
leak the pressure should not build or should build much slower.

Mark

Frank Condelli wrote:
>

>         If it were the top O-ring on the cylinder then why would the cooling
> system hold 30# of pressure for 30 minutes with no signs of leaking into the
> heads.  AND, why would there be no signs of air leaking into the cooling system
> when each cylinder was pressurised with 120# of air pressure?  I'm not
> convinced it's the water pump either BUT I'm looking for an answer and the water
> pump scenario as explained to me by others seems to be the most believable under
> the circumstances.
>
> Cheers
>
> Frank Condelli
>