GM 12551519 Housing, Engine Coolant Thermostat

Begin by draining about three quarts of coolant from the radiator until the level is below the thermostat housing. Disconnect the upper radiator hose from the thermostat housing cover. Remove the nuts/bolts holding the cover and lift it off. It may be necessary to move the belt tensioner bracket aside and tap the cover with a soft-face hammer to break the gasket seal. Note the orientation of the old thermostat and then lift it out. Use a scraper or putty knife to remove any old gasket material and sealant from the mating surfaces, being careful not to let any fall into the coolant passages. Clean the mating surfaces with lacquer thinner or acetone. Apply a thin layer of ATV sealant to the gasket mating surfaces of the housing and cover. Install the new thermostat in the engine with the correct end facing up. Position a new gasket on the housing, ensuring the holes line up with the bolt holes. Carefully position the cover on the housing and install the bolts, tightening them to the specified torque without overtightening to avoid distortion. Reattach the radiator hose to the cover and tighten the clamp. It is recommended to check and replace hoses and clamps at this time. Refill the system with coolant. Run the engine and carefully check for any coolant leaks.

Check the coolant level in the system. Verify the drivebelt tension is correct. Observe the temperature gauge or light operation. If the engine takes a long time to warm up, it may indicate a thermostat stuck open and needs replacement. If the engine runs hot, and the upper radiator hose isn't hot, it suggests a thermostat stuck shut and should be replaced. If the upper radiator hose is hot, it indicates that the coolant is circulating and the thermostat is open.