Rusty,

I found this in the archives.  This could be my problem.

Dave,
One thing that caused me a bunch of head-scratching was the bypass circuit
in the water pump housing when first filling the cooling system.  It can
prevent the wp impeller from pumping coolant through the engine.  That is
where I would look first.  Did you weld and/or plug the hole at the bottom
of the thermostat?  If so, you could have air trapped in that cavity.  If
you installed a screw-in plug, try removing it and then filling the system,
then replace the plug.  If you're running a thermostat, have you removed it
to fill the system?

Mark S.

Steve Brooks