quote:Originally posted by larryw:
If the re-circ bypass is plugged, does water circulate at all within the engine and heads prior to the opening of the thermostat?
the heater hose circuit will flow during warm-up with the T-stat closed if there is no heater control valve installed in the heater core supply hose from the block nipple, or if the valve is open
if the heater core return hose connects back to the water pump, the loop acts as a warm-up bypass. if the return connects elsewhere you'd need to determine if that coolant is recirculating through the engine or being directed to the radiator, but either way there's still ~some~ flow through the heads hopefully enough to prevent the hotspot condition you've described
with no internal engine bypass circuit, and no heater loop, the engine will experience dead head cooling system pressure against a closed T-stat and possibly hot spots in the heads
it's not a big deal to drill the aftermarket water pumps to open the bypass passage if you want to, you could even use a reduced from factory diameter to limit the amount of hot recirculating coolant
I can't imagine that the head gaskets are appreciating the temp fluctuations indicated by the gauge banging from side to side?