I have a 322 nailhead in my model A. I' m running a 190° thermostat (it's new). If the outside temperature is 50°- 60° the temp will rise to about 190° and drop. I assume I am seeing the thermostat opening. Then it hangs right around 150°. Why doesn't it go back up to 190° and stay there? Then, when it's 85° outside, again it raises up to 190° and drops. But now when it raised up again it wants to run at 210° or higher. So it's running too cold when it's cool out and too hot when it's warm out.
You may not have the radiator full and have air trapped,but I'm just speculating. What kind of car? what kind of fan? really need a little more information. HRP
A tstat will always break slightly higher on the first opening as there is cold water traped against it on the rad side.
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