Message text written by "Roy"
>The engine and radiator are interconnected by the upper and lower radiator
hoses. When the engine is off, coolant will still continue to circulate.
How
does this happen? It is called the thermosiphon effect. <
A thermosiphon works very well in a system designed to take advantage of
it. The Austin 10 uses a thermosiphon and has no water pump at all. I
think the Model T does as well. The Austin has the water outlet in the
center of the head and angle upward and forward to the top of the radiator
and the return hose exits the bottom of the radiator and enters the lower
part of the engine.
Now consider the SC engine (Hearld, Spitfire, GT6, TR6) with the coolant
outlet and return mounted side by side on the front of the head. There is
no thermosiphon here as the high points for both paths are at equal
heights.
Now consider the TR7 and TR8 with cross flow radiators. With the coolant
passages running horizontally there will be little circulation but to
density changes.
Quite frankly, I think that most engines cooling will occur with the fan
running due to the air passing across the exterior surface of the engine.
Anyway, who cares how long it takes the engine to cool down from 200 F to
185 F after you shut down? Certainly not GM who's Citation and other early
FWD cars had cooling fans running right off the battery (after the key was
off). They did it for the simplicity of the wiring. AUDI did it to cool
the turbo charger (which is a real issue). And as Randall Young pointed
out it can also help with a carburettor fuel boiling issue. But as far as
expiditing engine cool down once it is switched off is, in my opinion,
silly.
Dave Massey
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