Jim Grant's Tech Tips
'98 VW Jetta, Jumpy Temperature Gauge
Q:
My ‘98
VW Jetta TDI runs great...but lately (153k) I have noticed the temp gauge
has been "jumping around" often moving from the normal operating
temperature to very high and then back to normal. I have checked the fans
and they seem to be operating correctly and it does not boil over. Can
this be a bad thermostat or indicator? If so where is the signal being
generated for the temp reading on the dash? Or do I have another problem?
- Tom L.
A:
When the temperature
gauge is jumping is this at low speed in town driving or the high speed
of highway driving? The other question would be is just how fast is the
gauge moving/jumping? If a gauge is moving quickly, with little to no
rhyme or reason to vehicle speed or load, then I would be inclined to
believe that the problem is being caused by a faulty temperature sensor
or sensor connection. If the gauge is moving with reason and seems to
demonstrate a purpose of movement then there may be a thermostat or cooling
system problem. I would also suggest performing a visual inspection on
the coolant level. We have found that the coolant level sensor is not
always the most reliable beast for that type of simple information. Also,
you should know that the coolant temperature is easily monitored through
the diagnostic connector for the vehicle computer. Just plugging in a
scan tool can provide as close to real live coolant temperature information
that can be had. A test drive with a computer scan tool should answer
a lot of questions.
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