Few questions for all.
Never had a clutch fan from this era of my own, but worked in the radiator business in the late 60’s early 70’s. Do these 68 clutch fans have a thermostat on them. Many clutch fans from this era did and the “clutch fan” thermostat may be the problem.
Did the engine get bored as part of the rebuild? How much, .020, .030, .040?
As Steve noted, what is the timing at initial and at total with the engine at about 2,500 RPM? Are you exceeding 38 degrees of total advance? If so, are you running a stock distributor. Better yet is this the same distributor before the rebuild? Set at the same initial timing of say 6 to 8 degrees before top dead center?
Gee, did the car overheat before the rebuild??
Run a 180 degree thermostat for the water. Always put your NEW thermostat in a pan on the stove and use a candy thermo (that’s what my wife has) and bring it to a boil and ensure that it opens. I would even check the old one!
A rebuilt engine always will run a bit warm at first. Normal. I would suspect that after 500 miles or so, that would go away. A marginal radiator that worked with a long mile motor may be pushed over the edge with new rebuilt motor.
Nothing worse that a car that over heats in traffic. Ruins a wonderful day in the sun… No substitute for a fresh radiator. If you are not an originality freak, there are also aluminum replacements for you car. In my experience your brass one will do just fine, but that is another step up you can go. 390 Ford engines have always been les likely to overheat. In trucks a big block Chevy is far more prone to overheating that a Ford!!
Rob
