Typically thermostat's fail stuck open, not closed..

In any case, if you follow the lower radiator hose on the passenger
side of the engine bay, you'll see it turn up and into the block.  That
hose connects to the thermostat - so once you disconnect that hose, its
3 bolts (IIRC) to remove the thermostat housing (which contains the
thermostat).  IIRC, Nissan just sells the entire assembly, so just pick
up a new assembly and new gasket and pop it on.  Shouldn't take more
than an hour or so.  I would suggest draining the coolant from the
radiator to minimize spills.

Cheers,
Nirav
96 Max GLE, 122k

Whatever you do, do not run the car without a thermostat, because the
water could go so fast through engine and radiator that it will not
transfer the heat out, and the engine will overheat.  My boss found that
out when he thought his car would run cooler without thermostat (not).

A racing friend also discovered that when he cooked his motor.  He has
since learned that racers that remove the thermostat use a restrictor so
coolant flows through at the proper rate.

PS: My 11 year old 95SE has never had cooling problems.  I replaced all
hoses and belts at 60,000 miles even though there was nothing in the
manual about that, because nothing will ruin a hot day like a blown
radiator or heater hose.