Thermostat The thermostat is the wax pellet type. A jiggle valve (which improves air bleeding during water supply) is provided on the flange part. When the thermostat is closed, the circulation of coolant is stopped, thereby making warm-up faster. Operation When the temperature of the coolant is low, the valve is closed by the spring, with the result that the coolant circulates within the engine, without passing through the radiator. When the temperature of the coolant rises and reaches a certain specified temperature, the valve opens and the coolant also circulates through the radiator.
When the temperature increases further and reaches a certain specified temperature, the valve opens fully, allowing even more coolant to circulate through the radiator. Thus, in this way the degree of valve opening is varied according to the temperature of coolant, and the temperature of coolant is adjusted by varying the amount of coolant caused to circulate through the radiator. Thermostat Test To test the thermostat opening temperature, use the following procedure: Cooling System Heat Problems To check if there is a good reason for heat problems do the checks that follow: 1 . The indications of a heat problem are as follows: a.
High coolant temperature indicator light is on or needle of coolant temperature gauge is in red range. b. Coolant boils out (comes out because of too much heat) of the cooling system during operations. c. Coolant boils out on the floor when the engine is stopped. d. Coolant must be added at the end of each shift but Steps b and c are not present. 2 . If indication in Step 1a is only present. It is possible the problem is only a damaged gauge, light or sender. Make a replacement of the defective part. 3 . If indication in Step 1b is present, do the procedure that follows: a . Run the engine at medium idle (1200 rpm) for three minutes after high idle operation.
This cools off the hottest parts of the engine before it is stopped. b . Install a coolant recovery system on the truck, if not already equipped. 4 . If indications in Step 1b, 1c or 1d are present, but Step 1a is not and the high temperature indicator light does work, the problem can be a damaged radiator cap seal or there can be a leak in the cooling system. Complete the procedure that follows: a . Do the Pressure Cap Test, Cooling System Leak Check, Thermostat Test and Belt Adjustment in the Testing And Adjusting. b .
Clean the radiator with hot water (steam clean) at low pressure and use detergent or air according to the different types of debris that caused the radiator to be dirty (plugged). c . Check the engine high idle setting. W ARN I N G The pan, water and thermostat will be very hot and can cause burns. Do not touch the pan, water or thermostat. Handle the components with an insulated device for protection. 1 . Remove the thermostat from the engine. 2 . Hang the thermostat in a pan of water. Put a thermometer in the water. Put the thermostat completely under water. Do not let the thermostat make contact with the pan. 3 . Put heat to the pan of water. Make the water in the pan move around.
This keeps all of the water at the same temperature. 4 . The thermostat must start to open when the temperature is 82°C (180°F). The thermostat must be fully open at 96°C (205°F). G643 (E) Service Manual Chapter 3. Engine Mechanical System 54