20 psi & no leaks!
The Mityvac MV 4560 Cooling System Pressure Test Kit is an extremely useful tool. As soon as the pressure in the cooling system increased to 0.5 psi I detected (heard and saw) a leak between the upper and lower thermostat housing sections. Upon inspection I found that the flimsy paper gasket had misaligned when the two sections were pulled together when the bolts were tightened. When I installed the upper housing I questioned the need for the paper gasket since the stock housing did not have one. The system is designed to be entirely dependent on the thermostat gasket to prevent leakage. There is a tapered edge on the bottom of the upper housing that aligns it with the bore of the top of the bottom housing when the bolts are tightened. The edge presses against the thermostat gasket sealing the system. In my opinion the paper gasket defeats the original design. The thickness of the paper gasket reduces the pressure of the edge against the thermostat gasket. Since it also misaligns easily I advise against using it. Since I reused my thermostat gasket I applied a bead of RTV Blue along the edge of the upper housing where it mates with the lower housing. I let it cure for 24 hours after loosely tightening the bolts initially, then further tightening after 2 hours and 12 hours. My radiator cap is rated at 16 psi. When the pressure in the system reached 14 psi a slight leak occurred at the top of the lower radiator hose which was stopped by tightening the clamp. At 16 psi a leak occurred at one of the heater hose ends which was stopped by tightening its hose clamp. There were no more leaks even though I increased the system pressure to 20 psi and held it there for about 5 minutes.
