THERMOSTAT Replacement

The thermostat is located under the water outlet elbow at the radiator end of the cylinder head and is easily replaced. Drain the cooling system sufficiently to bring the coolant level below that of the water outlet housing. Disconnect the radiator top hose from the water outlet elbow. Remove the two bolts securing the radiator upper support bracket to the radiator cowling. Remove the nuts securing the water outlet elbow to the cylinder head, and lift off the radiator support bracket. Remove the water outlet elbow together with its gasket and lift the thermostat from its location in the cylinder head. Clean all old gasket material from the mating faces on the outlet elbow and the cylinder head before installing the new thermostat. Also ensure the thermostat seating in the head is clean. Install the thermostat with the coil spring side positioned downwards into the head recess. The radiator side of the thermostat is normally marked on the top flange. It is important that the thermostat be correctly positioned in the engine, otherwise overheating will result. Position a new gasket on the cylinder head face and locate the water outlet elbow over the thermostat. Fit the radiator support bracket in position and secure the bracket and outlet elbow with the three nuts and spring washers. Attach the bracket to the radiator cowling with the two bolts. Reconnect the radiator top hose and top up the system. Run the engine up to normal operating temperature and check for leaks. Recheck the coolant level once the engine has cooled down.

Testing

Inspect the thermostat for obvious faults. If the valve is stuck in the open position the thermostat is defective and must be renewed. To test the operation of the thermostat, suspend it fully submerged along with a suitable thermometer in a container of water. Both the thermostat and the thermometer should be suspended in such a way that they do not touch the sides of the container. Heat the water gradually and observe the action of the thermostat valve. Note the temperature at which the valve opens. The nominal temperature at which the thermostat opens is normally stamped on the base of the thermostat bulb. If the thermostat does not function correctly, it must be replaced with a new unit.