[jhein]

So if your motor is running at 150-165F for extended periods of time, that means your 180 t-stat must be opening at around 150-ish. The fact that it doesn't get above 165 would suggest that your cooling system is working well overall. Of course, that assumes your sender and gauge are correct. You could verify the temp with a infrared thermometer and test the t-stat in hot water to see where it opens. But if the temps are really 150-165, then no real need to test the stat because the operating temp tells you what you when it's opening.