Cooling System

Chuck Pierce cpcycle at
Wed Apr 9 15:32:00 EDT 2003

Mike Dell Tergo wrote:

>> 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?).

He afterrun system is to protect the turbo from excess heat when shut down.

> 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.
> Mike
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