Reference: Peter B. Water pump / air lock / Engine temp range....

[Bob Carriere]

If you are curious you may want to check the existing thermostat that you have..... and find out what setting it has..... of course you need to drain the block and drain some of the coolant...... while the radiator drains slowly and only half drained is OK..... start boiling yourself a cup of tea..... you know this HUP is a British design..... with your thermo stat removged and rinsed tie tring to it and suspended it in the hot water.....use your wife;s best cooking thermometer.....wait until the temperature of the water is near what the numbers are stamped on your thermostat..... if it says 185 F it should be fully open at that temperature AND returned to shutting when it cools. Some modern thermostat are design to open and stay open.... they call it fail safe position.... get rid of that and use a normal open old style thermostat......around 180 F........

If you do remove your radiator to have a radiator shop solder a threaded fitting for a steamline it might be a good time to have the radiator boiled out by the rad shop BUT do tell them to test for leaks at ONLY 2 or 3 pounds of pressure as these CMP radiators are not run under any pressure... ..meanwhile when the rad is removed try flushing the engine coolant core with some rad cleaner to see if you have any build up of rust sediment in the block........... on the passenger side....left side.... near the bell housing you should have a drain pet cock that allows you to drain even the lowest part of the engine cooling system...... it should flow slowly or you have deposit in the coolant passages...... try with a piece of steel wire to work it free... if not close the valve and wait for the next engine rebuild....

Sorry if Imissed correcting some typo Ihad too mcvuh wine with supper.....