Where is the thermostat? on 2000 Nissan Frontier

Where is the thermostat? The gauge goes all the way to the top when I am in stop and go traffic,when I start rolling again at a steady pace the needle goes right back to where it should be.

Asked by for the 2000 Nissan Frontier
Follow the radiator hose back to the engine you will find a coolant hose attached to a triangular flanged housing at the top middle of the engine secured by three bolts, thermostat is behind that housing.
I have a 2002 4WDR pathfinder. This description does not seem match my engine. The radiator hose splits before it hits the engine. The main branch stays on the left of the engine and goes straight to the firewall. A smaller metal tube splits off where the hose connects to a fitting on the tp left hand part of the engine and wraps around the front of the engine and bends down to connect to the block on the right side.
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Mine did this and I checked the water level. It was only a little low, but after i added water it hasn't done it since. Its been over 2 years ago.