Hummmm, just throwing this out there but same issue with two different brand heads? I assume the same brand housing/wp and thermostat? We all have our pet brands, could the hole in the thermostat not be bleeding?
No stat during test or dyno runs. No issue with Edelbrock heads, only the Trick Flow heads. We also tried a Shogun stand alone pump with the same results, so I'm reluctant to blame the water pump in this case. For all I know, there may be something hinky in the block passages that I couldn't see. No matter, I gave the customer instructions to purge the air and avoid overheating once he gets it in the car.
I had a issue on all of my W-type heads... I had a
piece of clear plexi tubing in the upper radiator
hose to see if water was moving... I would run the
engine(in the car) and get it to about 140* and shut
it down.. then turn on the pump(electric) and it would
start to flow..let the pump run about 5 minutes then fire
up the engine... once it purged the air it never had any
more issues unless I drained the water.. and had to do it
all over again... but the clear tube was a BIG HELP
