Early vehicles with no water-pump:'thermosyphon'

Up until around 1950, it was not uncommon to see cars using the
"thermo-siphon" principle to circulate hot water from the engine up into
the
radiator top-tank,..then as it cooled, it would drop down thru the
radiator
simultaneously displacing cooler water back thru the bottom hose into the
engine again.

Was this system as efficient as pump-assisted cooling? Dont know, but in
some old footage WWII stuff, you can see TS being used on trucks as well
as
Jeeps. One might guess, that the hotter the coolant is, the faster it will
circulate.

Jason