Thermostat location how do i locate and replace the thermostat on my 1997 chevy lumina v6 3.1

The thermostat is in a difficult position. Follow the upper radiator hose and it leads into the block under the throttle body. 
Remove the air filter assembly and you'll c what is the exhaust manifold crossover pipe right in front of the thermostat housing.
 NICE, it gives you very little room to remove the 2 bolts to the housing and once u remove those then you'll find you have the thermostat housing loose but because of that darn exhaust manifold crossover pipe u don't have enough room to take the thermostat housing out to change the stinking thermostat. 
So from what you can see, you have to remove the heat shield which is cased around the exhaust manifold crossover pipe and if you still can't get enough room to remove the thermostat, (which you amy find out)then you'll have to remove the crossover pipe as well just to change the thermostat. 
If you have to remove the crossover pipe then their are 2 bolts on both ends of the pipe leading into the manifolds. But then the tough parts done and once u switch the thermostat over and ATTENTION:remove any old gasket material and put a new gasket in it's place then installation is reverse of removal. 
Good luck and hope this helps,

Trace the radiator hose (upper first, lower next) back to the engine block. At the end of the hose it will connect to a housing -- thermostat is in there. Remove housing, note which way tstat is installed, put in new thermostat, etc.

You'll need a new gasket and need to clean old gasket off block/housing.