On your top main raidator hose there is a bubble looking piece. Take the bolts out of it and your thermostat is sitting in the engine block. To put a new one in get a new gasket and some silicone sealant and make sure not to overtighten the bolts because it is only an aluminum piece you are potting them into.
The thermostat on a Chevrolet Cavalier 1.7 diesel is located on the side of the engine. It can be found by following the upper radiator hose.
Should be in a removable housing at the engine end of the upper radiator hose
In the radiator in the front of the engine
Follow the top radiator hose from the radiator to the engine, where it connects is the thermostat housing, the thermostat is inside.
The coolant temperature sensor, on a 2005 Chevrolet trailblazer 4.2 liter engine, is located just above the thermostat housing. The thermostat housing is located in the front of the engine.
The thermostat in a 2.2L is located at the water pump wich is in the front lower left side of the engine
The thermostat is located on the left side of the engine. Look past the drive belt pulley and towards the bottom and you will see the thermostat housing and two hoses coming out of it.
The thermostat on a Chevy 2.2 engine should be located under the top hose inlet. The top hose as well as the inlet need to be removed to get to the thermostat.
You did not mention the engine size. Regardless, it is in the thermostat housing on the intake manifold.
Should be in a removable housing at the engine end of the upper radiator hose
Usually in housing at engine end of upper radiator hose
bottom of engine below ex manifold.