2000 GMC Sierra 4X4

[mikey531]

My 2000 GMC with 158,000 sits in the garage a lot. I started using it just to get it limbered up a little. It runs fine no issues other engine rap on startup. The temperature gauge always shows a little under 210 but in the last week it was at 185. I was getting plenty of heat and the temp would go up a bit when I turned off the heater blower. I am thinking either the fan is staying on or the thermostat is stuck open. However I am open to any other ideas too. Thanks!