Cooling system - K Series KV6 (Operation): Description and operation

Operation

General

When the engine is running, the coolant pump draws coolant through the pipe connected to the thermostat housing and pumps it through the outlet at the right front corner of the cylinder block and through the cooling jackets in the cylinder block, cylinder heads and inlet manifolds. From the outlet at the right front corner of the cylinder block, the coolant flows through the hoses and the coolant rail to the IRD cooler, the engine oil cooler and the transmission fluid cooler. From the top of the cylinder block, coolant flows through the outlet elbow and the top hose to the heater matrix. Coolant returning to the thermostat housing, from the cylinder block, the coolers and the heater matrix, bypasses the thermostat and flows back to the coolant pump inlet to begin the cycle again.

Coolant also flows through the expansion pipes to the expansion tank, from where it is drawn back into the system through the expansion tank outlet hose connected to the coolant rail. The increase in coolant volume, created by heat expansion, reduces the air space in the expansion tank, which pressurises the system and raises the boiling point of the coolant.

When the temperature of the coolant bypassing the thermostat is below 82 °C (180 °F), the thermostat remains closed and prevents coolant from circulating through the radiator. When the temperature of the bypassing coolant reaches 82 °C (180 °F), the thermostat begins to open, allowing 'cold' coolant from the radiator bottom hose into the pump inlet and hot coolant from the cylinder block to flow to the radiator through the top hose. The thermostat then regulates the flow through the radiator to maintain the engine at the optimum temperature. Maximum opening of the thermostat, and therefore maximum flow through the radiator, occurs if the coolant temperature reaches 102 °C (216 °F).

On NAS vehicles, operation of the thermostat is monitored by the Engine Control Module (ECM) using an input from the thermostat monitoring sensor in the bottom hose.

Coolant flows through the radiator, from the top of the RH end tank to the bottom of the LH end tank, and is cooled by air passing through the radiator. When required, the two cooling fans provide additional air flow through the radiator, particularly when the vehicle is stationary. Operation of the cooling fans is controlled by the ECM via the cooling fan ECU. The temperature of the cooling system is monitored by the ECM using inputs from the thermostat monitoring sensor (NAS only) and the Engine Coolant Temperature (ECT) sensor located in the cylinder block, to the left of the thermostat housing. ENGINE MANAGEMENT SYSTEM - SIEMENS (ALL EXCEPT NAS), DESCRIPTION AND OPERATION, Description. ENGINE MANAGEMENT SYSTEM – SIEMENS (NAS), DESCRIPTION AND OPERATION, Description.

Cooling Fan Control

The ECM controls the operation of the variable speed cooling fans via a Pulse Width Modulated (PWM) signal to the cooling fan ECU. The cooling fan ECU regulates the voltage of a common power feed to the two fans, and relates the voltage to the duty cycle of the PWM signal.

All Except NAS The ECM varies the duty cycle of the PWM signal between 10 and 90% to vary the fan speed. If the PWM signal is outside the 10 to 90 % range, the cooling fan ECU interprets the signal as an open or short circuit and runs the fans at maximum speed to ensure the engine and gearbox do not overheat.

The ECM operates the fans in response to inputs from: l The ECT sensor, for engine cooling. With the engine running, the fans come on at maximum speed if the coolant temperature increases to 105 °C (221 °F). The fans go off when the coolant temperature decreases to 102 °C (216 °F). l The instrument pack and the A/C pressure sensor, for refrigerant system cooling. AIR CONDITIONING, DESCRIPTION AND OPERATION, Description. l The EAT ECU, for gearbox cooling. AUTOMATIC GEARBOX - JATCO, DESCRIPTION AND OPERATION, Description.

If there is a conflict between requested fan speeds from the different inputs, the ECM adopts the highest requested speed.