Water pump stealth failure?

[Brett Dikeman]

On Sep 29, 2006, at 5:00 PM, Doyt W. Echelberger wrote:

> Temp gauge needle sitting just under the high mark with exp tank  
> coolant at
> 180 implies faulty reading for temp gauge.

The temperature gauge is reading perfectly normal- exactly where it  
should be.  This evening idling in traffic in the city during 60  
degree weather, the gauge was sitting smack on the fat line.   
Radiator and thermostat are recent, car has been run on the blue  
stuff for at least 60k.

> How does gauge work?  As actual coolant temp goes up, thermo sensor  
> warms
> and .....resistance goes up and somehow dash needle moves higher?

No- resistance drops, heating the bimetalic strip in the gauge MORE.   
The sensor fails by resistance going too high, or open circuit  
altogether; typical failure points are either inside the sensor when  
corrosion builds up between the thermoresistive "disk" and the brass  
body of the sensor, or the connector.

Brett