Toyota 90916-03109 Thermostat

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Before assuming the thermostat is to blame for a cooling system problem, check the coolant level, drivebelt tension, and temperature gauge operation. If the engine seems to be taking a long time to warm up, the thermostat is probably stuck open and should be replaced. If the engine runs hot and the lower radiator hose isn't hot, the thermostat is probably stuck closed and should be replaced. If the lower radiator hose is hot, it means that the coolant is flowing and the thermostat is open. Disconnect the negative battery cable and drain the cooling system. Follow the lower radiator hose to the engine to locate the thermostat housing. Disconnect the cooling fan switch and detach the hose from the fitting. If necessary, cut off the old hose and install a new one. If the fitting is deteriorated, the thermostat housing cover may need to be replaced. Remove the bolts/nuts and detach the housing cover. Note the position of the air bleed valve and remove the thermostat and old gasket material. Fit a new gasket over the thermostat if necessary. Install the new thermostat in the housing, making sure the air bleed faces up and the spring end is directed into the engine. Install the cover and bolts, then reattach the hose and tighten the hose clamp securely. Refill the cooling system and start the engine to check for leaks and proper thermostat operation.