Was working on the 'rolla today and noticed that at full operating temp, with radiator fan going off and on regularly, the temp guage was at about the 1/3rd position. It's usually at exactly the 1/2 position at full operating temp. Infrared heat gun says the valve cover is at about 175F at this time. Think the temp sensor might be failing?
the temp of the valve cover will have almost nothing to do with the temp of the coolant- what is the temp of the manifold next to the temp sender?
I checked that too, it was 168 or something like that.
Only real way to test this is to hook an independent temp gauge to the engine and find out what it is really doing...
Update: Had an autocross yesterday, in the middle of the event I noticed that the gauge was back at the 1/2 position. The manifold by the temp sensor showed 177F at that time.
Check the connection at the sender to make sure it is clean. Similar to what my Dad's Dakota does with the oil pressure gauge. Sometimes is reads low, but if you unplug and plug it back, gauge reads back in the normal position. Every so often he has to do this.
Update - I lost the motivation to check this since the problem had fixed itself, but I was working under the hood today and checked the connector, it was so filthy I was surprised it was working at all.
I would have thought an air bubble.. but glad it was just a filthy connector