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I kinda disagree with the fan clutch theory. I would believe that the engine would still warm up. The thermostat would just not open as much. I have had several peices of equipement that had overheating problems. We were able to adjust the fan clutches one way or another to keep the machine cooler. Several of them are almost running on a direct drive type of fan cooling. The engines still go up to normal running temp. They just don't go one degree warmer than the stock setting. Winter or summer. Every Ford that I have all basically run in the N to O range. The cooler side of the guage. Reguardless of engine size or truck model.
I could understand the guage being off but this still does not explain the heater not blowing real hot. Stumper.
I the meantime I found out that my low readings came from the thermostat. I changed mine (with the totally corroded housing) and my temp reading is now around the 'N'. Haven't noticed any significant increase in mileage, though (other than what I expected with the mods I put in ).
My pa always said a hot engine is a good engine. Of course, his is a dated theory from the 70's when he was a mechanic, but he talked how the piston would fit tighter in the cylinder and how everything just "came together" better when things are hot.
Nowadays, I would agree with a cool engine being top notch. I don't think it being cool will damage it in any way. It MAY decrease fuel economy and performance on a small scale, but I would say it couldn't be that noticable, if at all.
The biggest advantage that I would see in engine longevity.
I have owned several different ford trucks over the years and I have noticed that they all ran a little cold. Even the Ford car I own runs a little cooler than other auto makers.