testing coolant temp gauge sender for 80/90/4k/4kq/CGT

Huw Powell audi at mediaone.net
Thu Feb 21 14:19:44 EST 2002

> Conversely, you can check your dashboard coolant temp gauge by using a jumper
> to send 12V from the battery(ignition off!) through the sender wire -- it
> should be blue/brown(hey Huw, is this OK?).  I'll assume that this will send
> the gauge needle to the top.  If it does, time for a new sender.

thanks for the specs since I was too lazy...

but don't send 12v into that gauge from the sender wire!  The sender is
a varying resistance to ground, the gauge is supplied with a regulated
10 volts from the instrument cluster.

The "gauge test" is to substitute known fixed resisitors to ground in
place of the sender.  As you can see, 1000 ohms should produce no
deflection, 500 a bit, 100 should read hot, and less than that, say 50
ohms will pretty much peg the gauge.  A dead short to ground in place of
the sender will definitely peg the gauge.  Remember the gauge is heavily
damped (responds slowly) and will not read correctly for a little bit -
10 to 30 seconds?

Huw Powell



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