Classic/Antique Car Repair: Pontiac straight 6 cooling, flat six, thermostat

Question
I have a 1952 canadian built pontiac with a flat six. I have replaced the radiator, thermostat, waterpump.. The car gets hot instantly. Will pulling the water distribution tube help? The radiator has to come out right? If I flush the system is there an additive I should run through 1st? I am not a mechanic but not a novice either. Any help would be greatly appreciated...
Thanks

Answer
Hi Bill:
If the car runs hot instantly, that is usually a sign that
coolant is not circulating through the engine. Since you have
changed the thermostat, at what temperature is the thermostat
set to open? For a Six Cylinder small block, I'm guessing 160-190 degrees?
Check the temperature rating for the thermostat.

A GOOD TEST... Remove the thermostat and try running the car without it.
This will tell you immediately if the thermostat is the problem. If no
thermostat, the car temperature should NOT go up, as coolant is continuously
flowing through the engine.

If the thermostat checks out OK, There may be blockage in the engine somewhere.
A pressure flush should reveal and fix that. Since you have already replaced the water pump,
this is the only other thing it could be.