I have a Davies-Craig DCL14 on my 32 atm. Its causing me no end of hassles.
Firstly, I had to have the A/C fan rewired so that it comes on when the A/C is switched on (ordinarily thermo-switched from the switch in the bottom of the radiator), otherwise the gas over-pressurises.
With a FMIC, the engine is quite susceptible to overheating. I had it out at Winton the other week, and the gauge tried to wrap itself around the H mark. Took about 15 minutes idling with bonnet up to cool down again. Lots of coolant being blown across into the overflow bottle.
I'm seriously considering putting the factory fan and shrouding back on. Actually, have driven it in Adelaide in 40 deg heat in the factory configuration, black car, A/C going full blast, and the temp gauge never budged.
My advice would be to leave it as Mr Nissan designed it. The couple of rwkw you'll gain isn't worth the worry.
Ever considered that the thermostat might be faulty?