Cooling system - Td5 (Description): Description and operation

Description

General

The cooling system used on the Diesel engine is a pressure relief by-pass type system which allows coolant to circulate around the engine block and heater circuit when the thermostat is closed. With coolant not passing through the by-pass or the radiator promotes faster heater warm-up which in turn improves passenger comfort.

A coolant pump is mounted on a casting behind the PAS pump and is driven from the PAS pump at crankshaft speed by the auxiliary drive belt. The pump mounting casting connects with passages in the cylinder block and pumps coolant from the radiator through the cylinder block.

A viscous fan is attached to an idler pulley at the front of the engine. The fan is attached to a threaded spigot on the pulley with a left hand threaded nut. The fan draws air through the radiator to assist in cooling when the vehicle is stationary. The fan rotational speed is controlled relative to the running temperature of the engine by a thermostatic valve regulated by a bi-metallic coil.

The cooling system uses a 50/50 mix of anti-freeze and water.

A Fuel Burning Heater (FBH) is available as an optional item for Diesel engine variants. The FBH is located on the bulkhead and is connected in series in the coolant supply to the heater. The FBH is used to compensate for the relatively low coolant temperatures inherent in the Diesel engine. HEATING AND VENTILATION, DESCRIPTION AND OPERATION, Description.

Thermostat housing

A plastic thermostat housing is located behind the radiator. The housing has three connections which locate the radiator bottom hose, top hose and coolant pump feed pipe. The housing contains a wax element thermostat and a spring loaded by-pass flow valve.

Thermostat - Main valve The thermostat is used to maintain the coolant at the optimum temperature for efficient combustion and to aid engine warm-up. The thermostat is closed at temperatures below approximately 82°C (179°F). When the coolant temperature reaches approximately 82°C the thermostat starts to open and is fully open at approximately 96°C (204°F). In this condition the full flow of coolant is directed through the radiator.

The thermostat is exposed to 90% hot coolant from the engine on one side and 10% cold coolant returning from the radiator bottom hose on the other side.

Hot coolant from the engine passes from the by-pass pipe through four sensing holes in the flow valve into a tube surrounding 90% of the thermostat sensitive area. Cold coolant returning from the radiator, cooled by the ambient air, conducts through 10% of the thermostat sensitive area.

In cold ambient temperatures, the engine temperature is raised approximately 10°C (50°F) to compensate for the heat loss of 10% exposure to the cold coolant returning from the radiator bottom hose.

By-pass flow valve The by-pass flow valve is held closed by a light spring. It operates to further aid heater warm-up. When the main valve is closed and the engine speed is below 1500 rev/min, the coolant pump does not produce sufficient flow and pressure to open the valve. In this condition the valve prevents coolant circulating through the by-pass circuit and forces the coolant through the heater matrix only. This provides a higher flow of warm coolant through the heater matrix to improve passenger comfort in cold conditions.

When the engine speed increases above 1500 rev/min the coolant pump produces a greater flow and pressure than the heater circuit can take. The pressure acts on the flow valve and overcomes the valve spring pressure, opening the valve and limiting the pressure in the heater circuit. The valve modulates to provide maximum coolant flow through the heater matrix and yet allowing excess coolant to flow into the by-pass circuit to provide the engines cooling needs at higher engine rev/min.