'72 Temp Gauge Issue

[Stan B.]

Just prior to installing an original temp gauge and a new temp sending unit in my '72 I exposed the temp sending unit to 160 degrees and the gauge read about 100 - 110 degrees. I then expose the sending unit to about 300 degrees and the gauge read 165. What is going on here? I checked the resistance across the temp sending unit and all was fine at both temperatures. When I connected the new gauge I reinstalled the resistor across the east/west poles and the ceramic insulator across the north/south poles. Am I missing something? Thanks - Stan

[Jack H.]

Re: '72 Temp Gauge Issue

It's tough to respond when technical terms are 'made up' (e.g. 'east-west' terminals)... Plus, you leave out information for consideration (e.g. checked the temp sender resistance and it was OK).

This is a 'late' version of the temp gauge design. It was originally manufactured with the pointer needle installed, pointing toward the 'cold' side of the dial. At final test, the gauge was connected to a 'simulator' (provide working voltage and precision current to simulate a bona fide engine overheat situation...top of the dial needle position).

The test operator picked from a selection of wire wound, precision, shunt resistors to install on the gauge that would FORCE it to read correctly and the unit was considered finished/calibrated at that point. The shut resistor HAS to be properly installed and of the correct resistance value for THAT specific gauge for the system to work properly.

Also, in addition to serving the primary function of calibrating the gauge, it can act as a 'fuse' to protect the gauge in the event of a bona fide electrical overload situation. So, one shouldn't presume just because you have the original wire wound shunt resistor in hand, that it hasn't been damaged by prior owner guage episodes!

The attached picture shows the correct component 'stack up' on the back of one of these temp gauges... When the gauge is in good operation and installed correctly, a fixed resistance value of 100-115 ohms in place of your car's temp sender ought to correspond to a temp reading of 180F and a fixed resistance value of 50-60 ohms should give you a 240F reading.

[Stan B.]

Re: '72 Temp Gauge Issue

Sorry if I offended any members by using terms like "east-west" to describe two of the four posts located on the back of a temperature gauge and not explaining my problem in greater detail. My intention was to simply provide a posting that would be short and easy to understand. Using the same language, I posted my temperature gauge issue in a different forum and received a reply/solution within several hours.

[Michael W.]

Re: '72 Temp Gauge Issue

I'm from up north and understood your terminology immediately. Your post was not a west of time, that should be the east of your worries.