Perry, I too had a thermaostatically controlled fan (Kenlowe) in front of the rad on my 1967 4/4 and the cooling behaved like yours. I refitted the mechanical fan and threw out the thermostatical control. I now use the electrical fan only when the water gets reeal hot (100C+)by the switch.
Perhaps a daft question: have you checked if the fan turns the right way? Is it really pushing the air through the radiator and not trying to suck the air out of the engine bay? Kenlowes at least are built to work both ways and it is easy to get it wrong.
Frank
