Cooling system operation (Cooling system - L Series) (page 2 of 3)

The cooling system employed is the by-pass type, allowing coolant to circulate around the engine and the heater circuit while the thermostat is closed.

The thermostat is mounted on the lower end face of the oil cooler. The thermostat is located in the inlet side of the cooling circuit, which provides a more stable control of the coolant temperature in the engine.

When cold, the thermostat is closed and coolant is prevented from circulating through the radiator. Coolant is able to circulate through the bypass and heater circuits.

As temperature reaches 80-84 °C, the thermostat gradually opens, bleeding cool fluid from the radiator bottom hose into the cylinder block and allowing hot coolant to flow through the heater circuit and to the radiator through the radiator top hose, balancing the flow of hot and cold fluid to maintain the optimum operating temperature. When the thermostat opens fully, at 96 °C the full flow of coolant passes through the radiator.

An expansion tank is fitted to the right hand shock absorber mounting. Any excess coolant, created by heat expansion, is returned to the expansion tank through a bleed line from the top of the radiator. The expansion tank has an outlet pipe which is connected into the coolant circuit. The outlet pipe supplies coolant into the system when the engine is cool. This replaces coolant displaced to the expansion tank due to heat expansion.

The coolant is circulated by a rotor type pump. The pump is mounted on the rear face of the PAS pump which is driven by a drive belt. The mounting for the pump is sealed to a port on the cylinder block. The pump draws fluid from the oil cooler and and the heater circuit and circulates it through the the engine via the port on the cylinder block.

The radiator, positioned at the front of the vehicle, is a copper/brass cross - flow type with moulded plastic end tanks. The radiator is mounted in rubber bushes; the bottom of the radiator is located in the front body cross member, and the top is located in the bonnet locking platform. The top hose from the radiator is connected to the coolant outlet elbow on the front of the cylinder head and the bottom hose is connected to the thermostat housing.

For additional air flow through the radiator matrix, particularly when the vehicle is stationary, an electric cooling fan is fitted to the rear of the radiator. The temperature of the cooling system is monitored by the Engine Control Module (ECM) via signals from a twin terminal temperature sensor, which is mounted in the top face of the coolant outlet elbow. When a temperature of 106°C is reached, the ECM switches the cooling fan on via a relay. The fan switches off at 99°C. The coolant outlet elbow also houses a single terminal sensor which provides a coolant temperature output to the instrument panel temperature gauge.

All vehicles have two fans. These operate either in series or parallel according to engine coolant temperature or air conditioning requirements. The fan operation is controlled by the ECM. The fans operate in series (slow mode) when a temperature of 106°C or higher is sensed. When a temperature of 112°C is sensed the fans switch from series to parallel operation (fast mode). When the temperature falls to 106°C or below, the fans are switched back to series operation. The fans stop when a temperature of 100°C or lower is sensed.

The cooling system is also used to cool the engine oil, the Intermediate Reduction Drive (IRD) and the Exhaust Gas Recirculation (EGR) cooler:

An oil cooler is located at the front of the engine cylinder block. A housing at the bottom of the oil cooler contains the system thermostat and also provides the connection for the bottom hose from the radiator. A connection at the top of the oil cooler has two ports; one port supplies coolant from the cooler to the pump and the other port provides the by-pass circuit from the outlet elbow hose. Coolant from the radiator enters the oil cooler body through the thermostat housing and passes through the body of the oil cooler, reducing the engine oil temperature.