4ktq high oil temp update part 3

Huw Powell human747 at attbi.com
Mon Aug 26 17:37:12 EDT 2002

> As many listers had suggested, the real reason I was reading 150 C on my
> oil temp gauge had nothing to do with overheating at all.  I didn't
> believe it at first because I had played with my headlight dimmer and
> various other electrical circuits in the car with no appreciable change
> in the reading.  Yesterday while cruising home on the highway I finally
> realized that the gauge was going up a full 4 bars (roughly 20 C.) by
> turning the blower fan on full speed!
> I thought I had fixed the "problem" before by improving airflow to the
> oil cooler but I bet I just didn't use the fan that day and didn't see
> the gauge climb to the artificially high level.
> Interesting that it seems to be specific to that circuit.  I may try
> isolating the power for the gauge to a less noisy circuit or I'll just
> go with a different gauge.

I would bet that it is not the power side of the circuit that has
issues, but the ground side.  If the fan and the gauges share a ground,
and it is not quite perfect, ie, small resistance to "real" ground, the
high current demand of the fan will "lift" that slightly floating ground
up a volt or two, messing up the gauges reading.  I'm trying to
remember, of the three analog gauges in the coupe, which ones went up
and which ones went down when I had a similar issue (haywire readings
driven by the cig. lighter lifting the ground potential), but I can't...

Of course, either way, it is easy to test with a multimeter in your

Huw Powell



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