[TR] Fan Hookup

[Jim Muller]

On 11 Nov 2007 at 10:01, GHaynesTR4 at aol.com wrote the following 
sentences (not in this order):

> Eventually the sensor unit failed...
> If you retain the automatic-on/off feature, wire it to an
> always-hot circuit, so it can continue to run after the
> ignition switch is turned off, if the engine is still
> warm enough to require that.

This works as long as the sensor doesn't fail such that it keeps the 
switch closed, in which case it will run down your battery.  (You've 
already proven that an "inexpensive" switch can fail.)  But more 
importantly, the water pump won't be running so you won't get any 
engine cooling.  In other words, there is nothing to gain from wiring 
it this way, but something to lose.

> In my case, I removed the engine-driven fan blade, so the
> electric unit is all I have.

Just remember to watch the temp gauge and hope the gauge works 
properly.

BL used an electric fan on the last year or so of the Spitfire.  It 
came on through the ignition switch.  I don't recall if it was wired 
to the ignition or to the accessories, or if it perhaps had its own 
dedicated contact in the switch.  On my car a PO had disconnected the 
radiator sensor and wired a manual switch out of sight under the 
dash.  I reconnected the sensor (it may have been bad and I replaced 
it - it was so long ago I don't remember), and wired the manual 
switch in parallel with it.  That way it works automatically, plus I 
have the manual backup.  And when running slowly on really warm days 
I can turn the fan on before it comes on by itself, gaining a few 
minutes of airflow.

A fan should stay on after the engine is stopped only if something 
under the bonnet requires localized cooling.  My Fiat X-1/9 had such 
an insulated engine compartment that after I parked it on a warm day 
it could suffer vapor lock for the next 15 minutes.  Fiat's solution 
was a dedicated fan blowing on the carb, with its own thermostat.  It 
was disconcerting to shut off the engine and have a fan come on as I 
walked away.

-- 
Jim Muller
jimmuller at rcn.com
'80 Spitfire, '70 GT6+



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