The one at the bottom is the thermostat, have to replace the complete sealed housing. The elbow which is bolted to the inlet manifold and looks like it houses a thermostat is in fact empty inside and is just there to connect the large top hose from the radiator. It's a throwback from the early V8 engine design. Some of the 4.0 litre engines also have a temperature sensor screwed in to it. Get a new gasket first, remove the elbow and have a look to ensure that someone hasn't put a thermostat in there..if they have, remove it as it will seriously affec coolant circulation.