Stephen,
You may have a problem with your thermostat. My engine will hold at 85 - 90 from start up to running temp but if I give her a squirt or sit in traffic the temp slowly climbs to 110 and the thermo can just barely hold her. It's fine when on the freeway ie sits on 85 - 90 no problem but as soon as I get disruption of airflow or I sit behind traffic she climbs. I haven't had it boil from the radiator but I do find that after a longer trip and the car sits for a few minutes the block sometimes boils sending some coolant to the overflow. This seems to be indicatative of having too much bypass and the block is getting too hot.
The brass insert allows for the thermostat to block off the bypass back through the engine. Cooling is then directed more to the radiator. Without this insert you will be loosing more than 25% flow to the radiator. From all the forums I have read in the last couple of days it seems this insert is one part that is important and that you have the correct Thermostat for a Cleveland. The windsors are different as the thermostat comes off the front of the pump/engine. I am not sure of what setup the thermostat has. ie is it a bypass set up or does it bypass somewhere else. I believe windsors do not have this insert.
Jas,
I believe it is very very unusual for the brass insert to be missing. However, everyone I spoke with who new about clevelands said that some reconditioners/ engine rebuilders removed them if they were damaged (and then probably couldn't get one to replace
). I believe some were cast steel ones (and were probably buggered), the brass ones should be fine.
One of the keys for me was even if I stop and leave the thermofan on the temp didn't move down. I still expect the old girl to get a little warm when I am on the track and in heavy traffic / hot days.
Hope this helps.
TC