Cooling System: Description and Operation

Engine Cooling

COMPONENT LOCATION





OVERVIEW
Because of its powerful engine, sophisticated transmission and traction system; the vehicle in the most demanding conditions will need to continually dissipate as much as 120 kW of heat to atmosphere. To compound the situation this typically occurs at low speeds when there is insufficient air being forced through the radiator to aid the cooling system. With this in mind and considering that the majority of vehicles rarely need to dissipate more than 10 kW of heat, the cooling system has been specially developed to cope with the severity of off-road driving and variable extremes of climate.
The cooling system functions using the cross-flow principle. The coolant is routed from the coolant pump into the engine block on the exhaust side of the engine and leaves the engine block at the rear edge, via the thermostat housing, on the intake side.
The thermostat is a wax thermostat. The coolant temperature sensor is located in the thermostat housing.
The coolant is pumped from the coolant pump to the engine through 2 connections. After passing through the engine, some of the coolant exits the engine block at the rear edge of the exhaust side to be routed through the passenger compartment element and onwards to the coolant pump.









PRINCIPLES OF OPERATION
At idle, and low outdoor temperatures (lower than -10°C (14°F)) the engine's idle speed increases from approximately 650 rpm to approximately 750 rpm. This is to increase the coolant flow through the passenger compartment element, which, in turn, makes it possible to increase the heat in the passenger compartment. The coolant pump is driven by the power steering pump through a flange.

Coolant Flow - Closed Thermostat
Coolant leaves the engine block via the 2 circuits at the rear edge on the intake side of the engine.
- The coolant is routed from one of the circuits to the engine's oil cooler and onwards to the coolant pump.
- Coolant is routed from the other circuit to a 'by-pass' circuit where there is a valve. The valve is closed at engine speeds up to approximately 1500 rpm. At approximately 1500 rpm, the valve opens and coolant passes through the circuit. By keeping the valve closed at low engine speeds, a sufficient flow is guaranteed through the passenger compartment element to obtain a good climate (sufficient heat) in the passenger compartment.






Coolant Flow - Open Thermostat
- When the thermostat opens, coolant is also routed to the radiator
- The radiator has an inlet on the Right Hand (RH) side and 2 outlets on the left-hand side
- The greater volume of cooled coolant is routed at the radiator's lower outlet to the coolant pump
- At the upper outlet some of the coolant is routed to the automatic transmission's oil cooler. Before the coolant reaches the oil cooler, it passes a 'choke' circuit through the radiator with a lower (slower) flow than other coolants. This provides optimum cooling of the coolant before it reaches the oil cooler, which in turn, provides effective cooling of the transmission oil. The coolant is routed from the oil cooler onwards to the coolant pump.

Bleeding
The engine has 2 bleed circuits connected to the expansion tank. One is located on the radiator and the other on the cylinder head.

Radiator and Cooling Fan(s)
The radiator, which dissipates heat from the engine coolant and engine mounted oil cooler, is manufactured from a 27 mm aluminum matrix with high-pressure injection molded end tanks.









Dependant on climate conditions there are 2 specifications of radiator fan available:
- Cold to mild climates: a single fan unit designed around a 500W motor
- Hot climates: a twin fan unit features two motors delivering a total of 750W
Common to both fan types are:
- Electric motors with brushes
- The Engine Control Module (ECM) controls the fan speed via Pulse Width Modulation (PWM) signals to the Electronic Fan Control Module (EFCM)
- The fan speed is controlled at 4 levels:
- Run-on occurs in 3 stages (i.e. depressing the fan speed)
- The engine cooling fan is activated a certain time after the engine has been switched off to protect various engine components from overheating
- The time the fan is activated and the speed of the fan is dependent on the coolant temperature and the driver's driving style (engine load) when the engine is switched off
- The hotter the engine and the hotter the load, the higher the fan speed and the longer run-on time. The maximum time of run-on is 360 seconds
- The EFCM can, by modulating the PWM control signal, inform the ECM about the fan's status and any faults.
PWM control of the fan motor provides variable control of fan speed to ensure minimum fan noise and reduced energy consumption when fan operation is required. The control module is mounted above the wade water entry lines For additional information, refer to Electronic Engine Controls - 3.2L Electronic Engine Controls
The coolant expansion tank provides an expansion volume and permits easy in-service bleeding of the cooling system. Coolant level sensing is precise to provide early warning in the event of low coolant level. To prevent intrusion into the expansion tank's casing, which could be a potential leak path, a magnetic float within the tank activates a switch located outside the tank.