Where is the thermostat located on a 1991 Nissan 240SX?

Find the lower radiator hose, which is under the top hose running from the left side of the radiator to the engine.

The loswer hose should run into an L shapped housing which is bolted onto the motor. Remove the 3 bolts attaching the housing to the motor, the thermostat should be right there. When replacing the housing besure to use a liquid gasket or else you'll have a leak.

If you look straight down on your engine it right below a little to your left of your cam gears, its that tube that sticks out and goes to the left and to down below into your radiator. The tube is connected to a metal thing, you have to take off the metal thing and the thermostat will be inside.

where the bottom hose of the raidator connects to the engine.

ok clear this up. At the lower hose is a sensor not the thermostat, the thermostat is located on the front of the block running vertical and just left of the water pump.