I had a similar problem after I had my 351W motor rebuilt. The car ran really hot and I tried a different fan with a spacer and that did not help at all. A new fan clutch from WCCC and the original fan solved my problem and the car now runs with the needle in the middle of the gauge. It has been in the mid 90’s the last few days and I have not had any problems. The temperature sender is the original unit.
Andrew:,
My car, like yours, is a 289 (2V) with automatic, power steering, and AC. The engine was rebuilt back in 1995 (broken timing gear) and was rebuilt as stock as possible. The normal operating temperature, according the gauge, is not about 1/4" inch past dead cold on the gauge with the AC off in regular weather. With the AC on during hot weather, it will climb up to about half way, maybe a little more. I had another 289 AC equipped Cougar which always ran a bit hot, so I had the radiator on that one recored with a 4 core radiator so it would run cooler (and used the original tanks so everything fits right). Given the good results, I had the same thing done to my '68 and it seems to help slightly, though the '68 never ran hot. It also has a replacement fan clutch that I got so long ago I can’t recall anything about it. So, absent true temperature readings, my educated guess is that it’s also the sending unit.
Just to update this, I got a laser thermometer and found that my running temperature was pretty normal, around 190 (measured around the upper hose and thermostat housing). So it seemed that the sending unit was indeed the culprit. I was able to find an original Autolite sending unit and that seems to be pretty spot-on. Also, changing the fan clutch to the correct one probably helped too!
That said, the gauge did get kinda high when I was driving down the highway in 100 degree weather with the A/C blasting, but that shouldn’t be a big surprise. It got slightly past the “P” in TEMP. Otherwise, in normal conditions, the gauge now reads pretty close to the middle when the car is all warmed up. So I think at this point everything is as it should be!