Goodbye multifunction sensor!

Tony Lum tlum at
Fri Feb 15 11:11:53 EST 2002


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 thread size of the MF sensor is
M14 x 1.5 and I was searching for something to plug that opening and I've
found 2 solutions.  I found out by accident that the oil drain bolt has the
same dimensions.  Found a nice one with nylon washer at the local hardware
store's miscellaneous hardware section.  If the nylon washer doesn't work
for some reason, I can use the copper washer that usually comes with an oil
filter.  Note than when you do this, you eliminate the overheat switch

A second solution is provided by the kits that you use to adapt metric
fittings to NPT fittings to hook up pressure or mechanical oil pressure
gauges.  One of the adapters is a M14 x 1.5 outer thread with a 1/8 NPT
inner thread.  I intend to re-tap this to M10 x 1.0 in order to accept an
Audi p/n 049 919 501 B sensor used in most CIS-E engines.  This is the 2
pin white sensor that incorporates both the gauge sender and overheat
switch in one housing.  I've already used this sensor with success in my
urq when I replaced the boost gauge with a water temp gauge.

A special note to T44 owners contemplating this change.  The A/C climate
control head uses one of the signals provided by the MF sender, so this fix
may not be applicable.  If you never overheat the engine though, this
sensor never comes into play.  The T85 cars run the overheat switch to the
compressor control relay, probably to shut down the compressor during a
overheat condition and my guess is that the MF sender performs the same
function but to the A/C head instead.

- Tony
Lots of I-5 Audis

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