Water pump stealth failure?

[Doyt W. Echelberger]

Hello Jim.......
What _other_  evidence of overheating do you have, beyond the temp gauge 
reading?

180 in the expansion tank isn't a high temp IMO.

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

Temp gauge components are: thermo sensor, connecting wire, dash gauge.

How does gauge work?  As actual coolant temp goes up, thermo sensor warms 
and .....resistance goes up and somehow dash needle moves higher? IF this 
is how the system works, then maybe the sensor element is failing by 
increasing its resistance too much.

Can you test the thermo sensor that is powering the dash gauge?  Where IS 
the thermo sensor that runs the dash gauge?....in the radiator? In the 
block? I think I remember a multi-unit cluster coming off the head, near 
the front of the engine, about in line with the sparkers. The thermo sensor 
was encapsulated in a rubber boot. When I looked at mine, the boot 
contained moisture and corrosion of all the contacts. Corrosion could add 
resistance and bias the temp reading towards high. If you check it, be 
careful not to snap off any leads or damage any parts while removing the boot.

Can you replace the thermp sensor with a known good one? Can you remove the 
sensor and test its resistance cold, and then hot, and really see how it works?

Just some ideas...................hope you find some answers.

Doyt
87 5ktq
Ohio





 >>>>>>>>>>>>>>>>>>>>>>>>>>>
At 10:09 PM 9/28/2006, you wrote:
>............snip...............
>
>I drove the car on the freeway today about 50 miles total, ambient temp was
>90+ F, and the temp gauge sat just under the top mark when driving at
>highway speeds.  I measured the coolant temp in the expansion tank just
>before shutting down at ~180 deg F.  The fan came on during driving and shut
>down shortly after I shut the engine down.
>
>Thanks for your ideas.
>
>Cheers!
>
>Jim Jordan