Re: Overheating Problem

["Fred Munro" <munrof@isys.ca>]

----- Original Message -----
From: Christopher Ritchie <critchie1@hotmail.com>
To: <quattro@coimbra.ans.net>
Sent: Thursday, April 08, 1999 7:12 PM
Subject: Overheating Problem


> Leif Pedersen wrote:
>
> >If your '92 100 is set up the same as my '87 5ktq I would change the
> >thermostat ASAP.  I had similar warnings, occasionally the indicator
> would
> >flash due to low coolant (when the level should have been adequate),
> and
> >the temperature had just started to run slightly higher then
> normal.  300
> >miles from home, cruising at 70 mph, my engine started to ping
> lightly
> >going up a hill.  No over temp warning, just slightly above normal
> coolant
> >temperature.  Slowed down a little and pinging went away.  By the
> time I
> >hit the next hill it was too late, coolant steaming out all over.
> Blown
> >head gasket and cracked head.
>
> >I wondered for a while on why I did not receive more of a warning.
> When I
> >inspected the thermostat, it had failed shut!  With boiling water on
> the
> >stove it did not open even a little bit.  First failure that I have
> ever
> >had like that.  Without coolant circulating through the engine, I do
> not
> >believe that I was reading the correct engine temperature on the
> gage.
> >Everything seemed almost normal, but the engine was running a lot
> hotter
> >then the gages were telling me.
>
>
> The thermostat fails shut; the engine boils over; and,  the
> temperature gauge reads "just slightly above normal"???  No Auto-
> Check warning???
>
> I have always wondered about the coolant temperature monitoring
> system in type 44 cars.  After warm-up, my temperature gauge ('88
> 5KSQ) will vary between the 1/4 and 1/2 mark, depending on
> conditions.  When the gauge reaches the 1/2 mark, the fan will come
> on, lowering the gauge reading.  I understand that this is normal.
> But a thermostat is supposed to keep the temperature of the coolant
> in the block at a designated temperature.  Engines are designed to
> operate best at a specific temperature.  Where the gauge rises and
> falls, this leads me to believe that the temperature gauge is
> monitoring the coolant in the radiator and not the block.  This would
> also explain Leif Pedersen's experience.  Is this so?  Am I missing
> something?  This is nuts.  You would never know if your thermostat
> failed.
>
Hi Christopher;

    The Type 44 rad is relatively small and tucked away to the left side of
the car, so it doesn't get a lot of air flow even at speed. As a result, in
warm weather the fan is required to cool the rad at anything less than
highway speed. This cycles the coolant temperature above the thermostat
setpoint and this is the cycle you see on the temp gauge. The thermostat can
close to hold the engine temperature up in cold temperatures but once it is
100% open, the engine temperature depends on the heat transfer in the
cooling system, not the on thermostat.
    The temperature sensor is located in the coolant outlet at the front of
the engine. When the coolant is flowing, this gives an accurate measure of
engine coolant temperature. If the thermostat fails shut, the coolant does
not flow, and the temperature sensor would only pick up heat from convection
currents in the coolant. Since the sensor is located outside the engine
block, it will probably read lower than the actual temperature as Leif
observed.

HTH

Fred Munro
'91 200q  272k km