Tim,
the last time we covered the topic of thermostats, I didn't have a digital camera available. So now is a good opportunity to throw up some pictures of the proper thermostat for a 351C.
If the thermostat in your 351C does not look like the one in the pictures below, you have the wrong thermostat, and as Tim pointed out, your engine is constantly bypassing a significant amount of coolant from circulation through the radiator.
Happy New Year Tim.
George
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