[blucar]

As mentioned in the earlier comments to this topic, restrictive washers and/or cutting every other blade off of the impeller was very common in the 1950's, the thinking being that the twin pumps pumped the coolant through the engine to fast... Wrong
I have found it to be very interesting, that old habits die hard. When anti-freeze was alcohol based it had a boiling point of 180 degrees, therefore it was only used in the winter with thermostats and/or grille covers to warm the engines up.
When the weather warmed up, motorists pulled the thermostats and dumped the anti-freeze.... With out the thermostats engines ran hot going up a hill and cold going down a hill.. ergo a lot of cracked blocks and/or heads.
As a result of the old habits passed on to younger generations, the spring ritual was to dump the anti-freeze and pull the stat. I knew a lot of people that did that up through the late 1960's.
My father was a little ahead of the curve... The " Prestone-Zerex" containers stated "Permanent" so he quit dumping his "coolant" every spring.
I found that 3-4 lbs of pressure cap, 160/180 thermostat and a 50/50 solution of coolant did not stop my engine from overheating in traffic or on hills, however, the coolant did not freely pass out of the radiator via the overflow, then the engine would cool down to the set point of the thermostat.
A pressure cap raises the boiling point 3 dgr for every pound of pressure, a 50/50 mixture of coolant also has a higher boiling point than water.
I have found that one of the best automotive inventions during the past forty + years has been the coolant recovery tank..