Cooling System

Mike Del Tergo mdeltergo at
Wed Apr 9 21:52:22 EDT 2003

>Just think about this for a minute. The radiator fan normally kicks in when
>the car is not moving. So when you are running, the thermostat is what
>regulates coolant flow through the radiator(s) and tries to keep the
>coolant in a certain temp range. Using a lower temp thermostat will lower
>the running coolant temp.

Your statement bolsters my point, tstat regulates flow (as you said) but fan
has more direct effect on instant temps  (tstat cannot quickly change temps,
fan can.  If the tsat moved that quickly, what would be the point of an
after run fan/pump as the coolant couldn't flow if the tsat was closed
already?).  Possible correction, you often only hear it when the car is
stopped.  When moving I often see the alt needle drop or hear the relay
click (on other Audis)to let me know the fan is running.  That said why does
it cycle if warm car is stopped?  Air flow over the rad has dropped and RPM
has dropped thereby reducing water pump flow.  Have you seen the closing
action on a thermostat after it opens?, drop a coupla new ones in a pot.
They are pretty slow moving. Once they are open, they don't really close
linearly with temp drop.  For that matter they don't really open at exactly
a given temp, though close IME.  Granted this makes the lower thermostat
even lower, but it also makes the higher one pretty close to the lowers
fully open point.  Given that same physical size and flow characteristics I
still offer that when "warm" 80/87 arguments blend.
I will check mileage as SJM says this may suffer.  I may also plumb in a
delineated temp gauge and plot the differences.

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