[Lynn Eades]

Charlie, here are some thoughts. Some probably slightly off topic, but cooling system related:
Water pushed from the rad. into the overflow tank stays there until the engine cools and sucks said water back into the radiator. This is achieved because that pipe into the (overflow) tank goes almost to the bottom of the tank.
Most vehicles (Tony) used early in the war did not have pressurised cooling systems, just a plain filler cap. Fords, Chevs (ref. MB-C1) Dodge and most British trucks were like this. The pressure system was adopted during the war.
Overflow tanks work with both pressure and open systems.
Thermostats were alcohol filled (bellows type) these were usually wrecked if the engine boiled. (modern wax type are much better and fail when open)
Deserts are stinking hot in the day time but usually freeze at night necessitating the use of alcohol based antifreeze. (this lowers the boiling point of water)
Although Chevs had "steam pipes", if they were producing steam, they were already in trouble.
As Tony said, all the overflow tanks had to be vented. Any negative pressure in the system would collapse the radiator as it cooled.(assuming pressure had escaped)
The downward pointing breather pipe reduces loss from the system.
The cooling systems of the era contained a larger volume (for a given power output) of water, that had a "margin of safety" that modern vehicles dont have.
The top of most radiators stood high above the top of the engine, which was a hang over from the time of no water pump. They were called a "thermosyphon" system. The water circulates from the fact that the hot water moved to the top, constantly.
The thermostat is in the system to get the best out of your engine. The longest life and best power output comes from operating inside the designed heat range. So the thermostat is there to keep your engine hot. Cooling it is another departments responsibility.
Btw, you can see by the welding at the top of the can (2nd photo) that that can is local manufacture
A modern style radiator pressure cap not only holds pressure in the system, it also has a valve to let air (or coolant) back into the system as it cools. It's the little bit in the middle.
I hope this lot helps some people.
Check out the sole of the passengers boot.