When I restored my '37 I had to replace the head on the 216. The block drain was plugged so I commenced trying to clear it. After pulling the "freeze" plugs and removing the water pump, I had reasonable access to the water jacket through the top sides and ends. This is with the engine removed and on a stand. I was astonished that there was 3 to 5 inches of dense mud-like deposits throughout the jacket. I mention this only to emphasize that clearing the drain plug is good, but only a small fraction of the problem. I had borrowed a "Zoo gun" (named for city of Kalamazoo) which combines water and compressed air to remove deposits. This uses the radiator hose connections and it had only removed deposits for the forward 2 inches of the water jacket.
Over many days I was able to remove almost all of the deposits with a combination of long screwdrivers stuck through the various holes, flushing with water, letting it dry and vacuuming using a small hose duct taped to the vacuum cleaner, ect.
I don't know how that much crud could be deposited but I am told that antifreeze was not used that much back then (with it's associated anti-corrosive agents) water from a horse trough may have been used to replenish adding contaminents, ect.
During the restoration the radiator was cleaned so now I have a pretty clean system. I have no problems with driving in 110+ degree heat.
Kent
