How do you replace the thermostat in a 1990 Nissan 300zx?
Replacing the thermostat in a z isn't an easy job. The front part of the engine must be completely removed. Usually when you replace the thermostat you might as well replace the water pump and timing chain assembly. The step by step instructions can be found easily online at many sites.
The knock sensor on Nissan 300ZX non-turbo from 1990 thru 1996 is located below the lower intake manifold on the rear of the engine block. To replace the knock sensor the upper and lower intake manifolds need to be removed. It is always best to replace the knock sensor with a new one considering its major dissasembly.
The thermostat is located on the RH side (passenger side) of the engine, toward the front. A radiator hose goes into a housing. Looking down from the top, there are (normally) two sensors going into the housing. The thermostat is below these and the cover is held onto the block with three bolts. If you replace it, go with an original Nissan brand. It's worth any extra cost.