The thermostat in the Chevy Silverado 2500 could fail in two different ways. First, it could fail in the closed position. This restricts fluid through the engine and causes overheating. Second, the thermostat could fail in the open position. This allows unrestricted flow of coolant through the engine. This could prevent the Silverado from producing heat inside the vehicle. The flow of the coolant through the engine could be so fast that it prevents heat transfer from the engine to the coolant, resulting in overheating.
Remove the thermostat from the Silverado. To do so, place a drain pan under the petcock on the bottom of the radiator. Open the petcock by turning it counterclockwise with a pair of pliers and drain 2 gallons of coolant into the drain pan. Follow the upper radiator hose from the radiator to the location where the hose connects to the engine. The housing the hose connects to holds the thermostat. Remove the radiator hose from the thermostat housing on the top of the engine by prying the hose clamp loose and then remove the housing with a socket and ratchet. Pull the thermostat out of the engine.
Place the thermostat in a pot of water. Orientate the thermostat so it sits on the spring end. Place a cooking thermometer in the pot with the thermostat.
Heat the water until it reaches 190 degrees Fahrenheit. If the thermostat opens up by expanding upward, it works properly. If the thermostat does not expand, replace it with a new one.
Place the thermostat back into the engine with the spring end facing downward. Place a new gasket on top of the thermostat, placing the housing on the thermostat and bolt it into place. Reattach the radiator hose and drain the coolant back into the radiator.
