I have noticed this morning, when having my defroster on heat, that the temp gauge showed halfway & then went back to 1/4 of the way past cold. This happened about 5 miles from my house.
Any suggestions?

 

It could be reading accurately and indicating that you might have a stuck open thermostat. Perhaps more likely is that the temp sending unit is failing. At least on my '93 the sending unit is separate from the temperature gauge for the PCM. It's a 1-wire sensor near the thermostat housing. Perhaps equally likely is that the gauge in the cluster itself is getting wonky.

My truck had a new thermostat and a new temp sender and the gauge read at around 1/3 or a bit less when hot.

 

I'd borrow a non-contact thermometer (one of those "laser" ones) and see what temp the thermostat housing is; and work from that knowledge.

The gauges, as noted, are not very accurate. They can be repeatable, but I'd not trust them to tell me I have a problem too much.

RwP

 

Josh, as Ralph said, you could verify with a non contact thermometer. FWIW mine quit and went totally cold on the guage. Took it out and wire brushed. Started working again.