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.
should eather be at the top in to engine or on bottom hose coming from engine
Yes.
how to change a thermostat on a 1990 Nissan pintara
The "1990 Nissan 300ZX" was a very popular model in it's time. The "Card ID" website noted the carrying capacity of the "300ZX" was noted to be a hefty 1500 pounds.
A Nissan 300ZX? No
http://www.zshop.net.au/Z32tech.htm
On the underside, passenger side, of the transmission.
226
it is located on the transmission itself
wheel
No, you will die.
3494 lbs on the Twin Turbo.