head gaskets they all do it i have two 99 sts with the same problem cost about 2500 to fix correctly.
Follow the upper raditor hose from the raditor to the motor, the raditor hose is connected to the thermostat housing, take the houseing off, the thermostat is under the housing.
Follow the upper raditor hose from the raditor to the top of the engine.Where the upper rad hose ends on the engine is where the thermostat is.
The thermostat is going to be located in the raditor. Use extreme caution when taking the raditor cap off to advoid burns from boiling antifreeze. Once the raditor cap is taken off you shuld see the thermostat. Just pull out to remove, or push hard to install.
the thermostat should be on the upper raditor hose on the intake
u didnt mention what size engine..either way just follow the upper raditor hose from the raditor
Look in at removable housing at the engine end of the upper raditor hose
follow top raditor hose to intake ,its inside cover.
it should be under the upper raditor hose look for 2 bolts that should be it
below the raditor hose that's connected to the thermostat.
On the 2.5L V6 the thermostat is located under the housing where the lower raditor hose is hooked the the engine.
follow the raditor hose it will have to bolts look for the bolts take them off and it inside the hose.
follow the top radiator hose to the engine. it should be under the cover where the hose attaches to the motor. follow the hose on top the raditor , it will lead you to the thermostat