Starting about 2 months ago only very occasionally, and now on just about every trip, the temp needle rises above the midpoint dot. I can drive along for half an hour with no problems, and then in the course of about two minutes the needle will rise from the midpoint dot almost to the red zone. Sometimes it will occur after driving for 5 minutes, other times not al all. If I pull over it will return to normal - sometimes in less than a minute, other times after 3 or 4 minutes. Sometimes it seems that turning the heater on full blast while continuing to drive will lower it as well, but not always. I checked the radiator hoses last time this occurred - when the temp guage read high, the top one was hot, the bottom was not. After the gauge dropped again, the top one was still as hot, the bottom one was warmer then before. When I started driving again, the gauge actually "bounced" - meaning it went from normal to hot over the course of about a minute, then back down again over the course of another minute - three times before settling in at normal again.

The thing that's bothering me here is that the behavior does not seem consistant - sometimes turning on the heater will work, other times not, etc. At first I was thinking my thermostat needed replacing, now after going through the archives I'm wondering if it is the temp gauge circuit board - which according to receipts was already replaced by the PO about 2 years ago - or something else... I did just remove and re-install the instrument cluster, though the sudden increase in problems this week didn't coincide exactly with that. I suppose I could just replace the thermostat to rule that out. Anyhow, any insights would be greatly appreicated!