I'm not sure how you're plumbing your cooling system, but if your remotely mounted thermostat doesn't have a small amount of coolant flowing past it, it could remain closed well past the point of engine overheating. Without some coolant circulation, it won't be getting the hot engine coolant near enough to it to open when it should be opening.

Hopefully you've already planned for this...

95 Montero SR
3.8 MIVEC, Advance headers, 2 1/2" exhaust, Magnaflow muffler, OME shocks & rear springs, 2" body lift, 3" tank lift, 4.90s, TRE front locker, factory rear locker, Roger Brown Rock Sliderz, 315/75r16 (35") tires, Sport big brakes