427 SO overheats and loses water

[chas427fe]

Tester came in and I started by pumping the system to 20 PSI, after 5 minutes no loss of pressure. Released pressure and started engine. after
4 minutes 150 degrees 2 PSI
6 minutes 175 degree 2 PSI
8 minutes 185 degrees 5 PSI
10 minutes 185 degrees 8 PSI
12 minutes 185 degrees 9 PSI
14 minutes 185 degrees 9 PSI
16 minutes 190 degrees 11 PSI
18 minutes 195 degrees 12 PSI
20 minutes 195 degrees 12 PSI
Gauge stayed steady during this. Engine ran at slow idle until I blipped it at 8 minutes and then it ran at 1200 RPM.

All this was done in my garage so there was no air circulation to help cool it.

Any ideas? Chas

[wtm442]

OK in the garage, but what about stop & go traffic - a real killer.

What thermostat - 180? 195?

Do you have electric fans with temp switch? If so, is it working correctly?

You may have had an air pocket after the first problem which made it look worse than it was.