Goodbye multifunction sensor!

[Brett Dikeman]

At 11:11 AM -0800 2/15/02, Tony Lum wrote:
>All,
>
>I posted a few days ago that the MF sensor in my 87.5 coupe GT failed in
>its typical mode-shorting the overheat switch and causing a false warning
>on the instrument panel.  I quickly discovered that the temp gauge sensor
>is actually run by the usual single temp sender,  Audi p/n 035 919 501, so
>I just unplugged the MF.  I also was looking for a way to get rid of the MF
>because its starting to weep coolant.

The sensor body is solid machined/cast brass; it's NOT the cause of
the leak.  It is leaking because it is not tight enough, or the
threads on the sensor or block are damaged.  Coolant isn't going
through the sensor or anything.

That sensor does three things.

-drives the coolant gauge.  Always has, always will, at least on the
type44's.  It would be fairly silly for Audi to NOT drive the gauge
off that, since all the multifunction temp sensors have this
functionality -anyway-...it would be unnecessary and duplicative.

-sends a signal, same as a low coolant sensor, if the car overheats.
This is the flashing red thermometer which indicates either low
coolant, or overheating coolant.  Either is considered a
coast-to-a-stop-and-shut-the-engine-off-now condition.

-sends a signal to the ECU and climate control via a second switch(it
is actually a separate set of contacts from the previously mentioned
function, inside the body of the sensor.)  The ecu goes into
limp-home mode(for example, in turbo cars, the wastegate frequency
valve gets turned off so the engine makes as little boost as
possible) to minimize the amount of heat generated by combustion; the
CC head switches off the CC clutch to get as cool air as possible
through the radiator.

Removing this sensor would be a -very- bad idea.  The whole point is
to warn you BEFORE the car physically boils over and blows a hose,
head gasket, or whatever(like, say, causes the head to warp; just
because you shut off the engine doesn't mean it starts cooling down;
rather the opposite, all heat in the hot internal parts spreads out,
and there's no coolant circulating around, and in this case, there
might not be coolant in the head at all.)

Brett
--
----
"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin
http://www.users.cloud9.net/~brett/
http://www.users.cloud9.net/~brett/bdikeman.asc	(PGP Public Key)