If its the 1800 20v the thermostat is located on the back of the cyl head up at the bulkhead. Follow the top rad hose until it connects to head, this is the stat. This is not an easy task for an amateur mechanic.
It is behind the water pump on the side of the block. It is easier to jack up the front end, remove the wheel on the side that the pump is on and go through that way. Once the pump is off it is right behind it.