100CS & pig roasts & overheating

[Phil@sievers.com (Phil Payne)]

In message <Pine.A32.3.91.970616080721.46012A-100000@gnu.uvm.edu> "Louis A. Mulieri" writes:

> Boy, so would I.  But if the thermostat is not controlling the
> temperature while operating what is?  Is it  open loop without the a/c
> with it's mandatory radiator fan?

I suspect the engine thermostat _will_ close sometimes, especially if
you're cruising without much engine effort on a cold day.  But, for
instance, no thermostats are fitted _at_all_ to cars exported to the
Gulf states.

The main cooling control system is the radiator fan - switched by a
three-position thermoswitch at the bottom of the radiator.  The
difference in a/c cars (rare in the UK, BTW) is that the first stage of
the fan is always on.  There are still two more levels, that come on if
things get warm.

Engines produce a lot of heat.  When stationary and idling, the fans cut
in and out quite frequently - enough to make adjusting idle a stop/go
process.  The ur-quattro does not have enough dissipation power, even
with the fan running, to cool an engine running under load - on a dyno,
_huge_ fans are needed to cool the thing.  This is normally done by
airflow.  You'll often notice the effect of a long freeway run followed
by a wait at the top of an exit ramp - instant personal Jumbo jet.

One difference seems to have been a wiring change to some cars moving
the power takeoff for the fan to a circuit switched by the ignition.  On
my cars, the fan circuit is connected (unfused) directly to the battery
- on many later cars, the circuit is switched through the ignition so
that fan can't run with the ignition off.  The system works the same
way, but there's no afterrun.  Too dangerous for amateur mechanics,
perhaps.

(At the Woburn event, one 20V driver asked us to find the "ticking"
 noise from the front of his car.  Intermittent for the last several
 hundred miles - not related to road speed or engine speed.  It
 turned out to be the fan, cheerfully fraying the front left brake
 pipe.)

--
 Phil Payne

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