96 Country 4.0L, 4WD, 265K, just installed used stock alt (N. Denso) from salvage yd - replacement alternator performs just like prior stock alt that lasted a long time.

Voltage gauge has always (purchased with 95K) been just a little erratic: at times when the battery is fully charged and low load on system, gauge will show slightly above 14 volts (maybe 14.25 volts if gauge is linear). At other times, same situation would show slightly below 14 volts (maybe 13.5 volts, again if gauge is linear), which would seem to be the normal, good situation. Above vs below 14 volts, about 50-50.

Load does not seem to impact the above-below 14 volts output.

Jeep has been doing this a long time. Nothing serious, just curious. One system that could be involved is the battery temp sensor?

Thanks in advance.
Larry

 

Don't overlook the obvious - a flakey gauge. Might also be a bad ground for the gauge.

I suggest using a good known gauge as a comparison.

 

Or the alternator isn't grounding well through the mounting bracket.

 

What's the purpose of the battery temp sensor? I would guess that if the XJ is slightly cooking the battery with just too many volts and battery is hot, the feedback loop will tell the voltage regulator and it will back off. That said, can the battery be protected from a voltage runaway situation? Can the battery temp sensor loop disco the alternator from charging the battery?

 

BATTERY TEMPERATURE SENSOR TESTING
To perform a complete test of this sensor and its circuitry, refer to the appropriate Powertrain Diagnostic Procedures manual. To test the sensor only, refer to the following:
(1) The sensor is located under the battery and is attached to the battery tray (Fig. 1). A two-wire pigtail harness is attached directly to the sensor. The opposite end of this harness connects the sensor to the engine wiring harness.
(2) Disconnect the two-wire pigtail harness from the engine harness.
(3) Attach ohmmeter leads to the wire terminals of the pigtail harness .
(4) At room temperature of 25° C (75-80° F), an ohmmeter reading of 9,000 to 11,000 ohms should be observed.
(5) If reading is above or below the specification, replace the sensor.