I have a 68 conv with a 289 all stock. I recently replaced my thermostat to a 180 when I re-built the heads. My temperature guage has been running at 7/8 or almost pegged. However, an infrared thermometer taken on the heads, thermostat housing and radiator all show 175 to 180 degrees, so I know I am not overheating. Any ideas why the guage is suddenly showing higher temps when it never did in the past....by the way, what is the normal operating temp for coolant? Thanks for any suggestions. P.S. I have already replaced the sending unit.

 

Thats nowhere near overheating. You're thermostat is supposed to stay closed until the water gets to the temperature that its rated at. Then it will open and let the water flow through the rad. untill the temp drops enough to close the thermostat.