temp guage - final

[jdouglas@mitre.org (jason douglas)]

Thanks for the advice on the coolant temperature guage.  The problem turned
out to be the sending unit ("multi-function sensor"), which failed but not
in the most common way.  Instead of failing completely, so that there was no
coolant temperature reading, it read consistently high - even when the car
had sat unused overnight.  Even more interesting was the way it failed -
after working satisfactorily since leaving the factory, it read high (but
not unreasonably so for several days before failing completely).  This lead
me to change the radiator fan thermo switch when it was probably ok.  I
guess that doesn't hurt at 100 k miles.

Other things to check: grounding and the output from the voltage stabilizer
on the instrument panel.  You can also check this voltage from the brown
wire on the connector to the temperature sender itself - it must be between
9.75 and 10.25 volts.

Halsey had the best price by far at $46.  It wasn't clear, however, if this
was the original style or the revised part.  Since my original part lasted
99 k miles and almost 9 years, I figured it was good enough for me.  My car
also needed a new plug for the sender, as a minute coolant leak had corroded
the terminals severely.  Shokan offered a plug for $20, but the local dealer
sold me one for <$2US and a couple bucks for the terminals (crimp onto the
wire and insert into plastic plug).

BTW, the new sensor deflects the guage considerably less (more than a tick
mark) than the old at my reference temperature (when the fan starts
operating at stage II).  Its interesting that there is so much variation
(how much is due to manufacturing differences and how much to aging of the
original sensor?)  I wonder if some of the recent discussion about
differences in operating temperatures (e.g., with Ur Quattros) is
complicated by these sorts of variations.

Jason Douglas