The car has always run pretty cool. In fact I don't think the temp gauge has ever made it more than 1/4 of the way to N, and that is the middle of the NC summer. Normally the temp gauge won't get above C. I checked the temperature sender and it was working fine. You can test it by just making a circuit with it and the temp gauge should go to H. The sender seemed fine. I pulled the thermostat, it was rated 180 F. It also worked OK when I dropped it in a pot of boiling water. I also have another one that I ordered from VB. This one is rated so 195 so I decided to experiment. First of all, the new one also worked fine. One difference was that the 180 F thermostat opened much wider than the 195, so it would provide much more rapid cooling.
OK, so I went ahead and swapped out the thermostats, and went for a long drive. First of all the temp gauge moved!! Very quickly it moved to the left of N, and pretty much stayed there all the time.
Well a few things...
First, the car reaches operating temperature much more quickly. This means that I can put the choke in more quickly. This will save gas, reduce emissions, and result in less running rich which can coke up the engine.
Second, the car is now running at a higher temp, and within reason, a hotter engine is a happier engine in that it will run more efficiently, and in fact generate more power.
The results were quite dramatic, the car drove much better and performance was better as well. Its amazing what a $5 part can do.
I am running a 195 thermostat, which I might need to replace in the summer with a lower temp rated one, but I think that the old one was opening too much and letter too much coolant flow through the engine.
For an excellent discussion of thermostats, see this site..
The key point here is that a fully functioning thermostat doesn't prevent the car from overheating. As the car gets hotter the thermostat will be wide open and the radiator is working flat out. The thermostat does provide a minimum operating temp, unless of course it is sticking open, in which case the min temp is going to be too low.