Silly is exactly right.
Chrysler had a heat soak problem in most of their mid '80's cars and
thought that the best way to solve the probem was to allow the fan to run
for 10-15 minutes after ignition shut-off. Only contributed to the problem.
Their cure was a 'thermister' (Chrysler's term) in
line with the fan. When the inevitable problems surfaced with this
arrangement, the mechanic's best route was to cut out the thermostaic
control and wire the fan directly to the ignition.
BTDT.
Also, GM had a cooling problem with a recent Corvette engine and Lo, out
comes the reverse-flow thermosiphon effect- the only way they could get
these motors to behave w/o overheating. Now, my Triumph has never
overheated- unless I have failed to check the coolant level. :) Gee, is
older better, as far as I'm concerned.
Jeff Johnson
'76 TR6
At 09:02 AM 4/5/01 -0500, David Massey wrote:
>
>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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