Description
Engine Cooling
COOLANT CIRCUIT FLOW
Coolant Flow Schematic Diagram
When the thermostat is fully open, the by-pass circuit is closed and allows maximum coolant flow through the radiator system to provide maximum engine cooling. From the water outlet the majority of the coolant is passed through the radiator and the transmission fluid cooler to the water pump, with a proportion still passing through the turbocharger, heater core and engine oil cooler.
When the thermostat is open the coolant flow from the radiator bottom hose passes through a venturi. This venturi creates a depression which pulls coolant through the transmission fluid cooler. The upper section of the radiator provides low temperature cooling of the engine coolant for the transmission fluid cooler. In hot climates an additional transmission fluid to air cooler is located in front of the radiator and A/C (air conditioning) condenser.
The degas tank accommodates expansion of coolant due to temperature changes and provides a secondary function to extract air from the coolant. A small proportion of the coolant flow is diverted to the degas tank via the bleed line connected to the RH (right-hand) radiator end tank. This provides a continuous degas function, independent to the thermostat position.
THERMOSTAT
The thermostat is closed at temperatures below approximately 82°C (179°F). When the coolant temperature reaches approximately 82-90°C (180-194°F) the thermostat starts to open and continues to open to the fully open position as the engine operating temperature increases. In the fully open condition the full flow of coolant is directed through the radiator.
COOLING FANS
The cooling fans are operated by a fan control module which is located at the rear of the LH (left-hand) cooling fan motor. The fan control module regulates the voltage, and subsequently the speed, of the cooling fan motors in response to a PWM (pulse width modulation) signal from the ECM (engine control module). The ECM (engine control module) calculates the required fan speeds from the engine temperature, A/C (air conditioning) system pressure and transmission fluid temperature. Under hot operating conditions, the fans may continue to operate for up to four minutes after the engine has been switched off.
The speed of the cooling fans is also influenced by vehicle road speed. The ECM (engine control module) adjusts the speed of the cooling fans, to compensate for the ram effect of vehicle speed, using the CAN (controller area network) road speed signal received from the ABS (anti-lock brake system) module.
COOLING SYSTEM COMPONENTS
Water Pump
The water pump is located at the front of the cylinder block. The pump is located in a recess in the block and secured with 3 bolts and sealed with an O ring seal.
A pulley is attached to the pump flange with 3 bolts. The pulley is driven off the FEAD (front end accessory drive)belt at engine speed.
Radiator
The radiator is a cross-flow type with an aluminum core and plastic end tanks. The radiator uses brazed aluminum tube technology to reduce weight. A low temperature zone is located at the top of the radiator and provides cooled coolant for the transmission fluid cooler.
The radiator is located in the vehicle by serviceable locating spigots and supports integrated into the end tanks. The supports are installed in rubber isolator bushes in the lower support bracket. The upper mounting of the end tanks is via a cross-strut attached to the vehicle body.
A drain plug is integrated into the bottom of LH (left-hand) end tank. Coolant outlet and inlet connections are incorporated into the LH (left-hand) and RH (right-hand) end tanks respectively. The LH (left-hand) end tank also has a connection for coolant outlet to the transmission fluid cooler.
Cooling Fans and Motors Assembly
The cooling fans are located behind the radiator in a shroud which is attached to the radiator with 4 plastic clips.
Two cooling fans are used for both engine radiator and A/C (air conditioning) condenser cooling. The fans are mounted in the fan shroud and each retained with 3 screws.
The cooling fan control module is also mounted on the shroud, behind the LH (left-hand) fan motor. The shroud incorporates 4 speed flaps, which pivot open to allow engine compartment cooling at speed.
The shroud, fans and module are supplied as one assembly and individual parts are not serviceable.
Degas Tank
The degas tank is located in the RH (right-hand) side of the engine compartment. The tank is located by a grommet on its underside and positively secured with a bolt and washer to a bracket on the vehicle body and a second bracket that locates in a molded slot in the tank body.
The degas tank has 2 connections; one for coolant expansion via the radiator overflow and one for coolant inlet into the thermostat housing. The overflow pipe is secured in the tank with a plastic clip. The hose to the thermostat housing is a quick release connector, retained with a spring clip. A third connection adjacent to the overflow connection is not used and sealed with a blanking plug and O ring seal.
A coolant level sensor is located in the underside of the tank body. The sensor reacts to the influence of a magnetic field. A float, with integral magnet, is located inside the tank, over the sensor tube. The sensor has contacts inside the tube, which are normally open. When the fluid level reduces, the magnetic float moves down the tube. When the magnet reaches the sensor contacts, the magnetic field closes the contacts. The sensor is connected to the CJB (central junction box) which receives the signals from the sensor. Maximum and minimum marks are molded on the tank body.
The degas tank provides the following functions:
- Service fill
- Coolant expansion during warm-up
- Air separation during operation
- System pressurization by the filler cap.
Thermostat Housing
The thermostat housing is located on the LH (left-hand) side of the engine block. It is secured to the block with 3 bolts and sealed with a gasket. The housing contains a wax thermostat which controls the coolant flow during engine warm-up. The thermostat and housing are supplied as a complete assembly and the individual components are not serviceable.
The thermostat allows rapid engine warm-up by preventing coolant flow through the radiator when the engine is cold. As the coolant temperature increases to approximately 82°C (180°F), the thermostat begins to open, the radiator coolant flow is balanced between the bypass and radiator up to the point where the thermostat is fully open at approximately 97°C (206°F). At this point maximum radiator coolant flow is achieved to provide maximum cooling.
Water Outlet
The water outlet is located on the rear of the cylinder head, below the vacuum pump and the high pressure fuel pump. The outlet is secured to the cylinder head with 4 bolts and sealed with a gasket.
The water outlet has 4 outlet connections; one from the radiator top hose, one to the heater core, one from the turbocharger and one for the cooling system by-pass hose.
An ECT (engine coolant temperature) sensor is fitted in the water outlet. The sensor is a push fit on the outlet and is sealed with an O ring seal and secured with a spring clip.
On NAS market vehicles a second ECT (engine coolant temperature) sensor is located in a Y piece connector in the radiator bottom hose. The NAS vehicle uses both sensors to measure ECT (engine coolant temperature). The additional ECT (engine coolant temperature) sensor provides thermostat monitoring for OBD (on-board diagnostic)'s.
Transmission Fluid Cooler
The transmission fluid cooler is located on the LH (left-hand) radiator end tank. The cooler bracket has two lugs which locate in corresponding lugs on the end tank. The cooler is positively located by a self tapping screw at the top of the bracket. The fluid cooler is an aluminum housing comprising louvered fins and plates. The plates allow a cross-flow of transmission fluid and engine coolant through the cooler.
The plates are immersed in engine coolant from the 'cold' side of the radiator which provides cooling of the transmission fluid by the temperature differential between the transmission fluid and the engine coolant. The transmission fluid cooler receives engine coolant from the low temperature zone at the top third of the radiator. The engine coolant flow through this section of the radiator is restricted by the transmission fluid cooler. Therefore the engine coolant has a slower flow rate across the cooling tubes of this section of the radiator. This cools the engine coolant more than the lower part of the radiator and consequently provides increased cooling of the transmission fluid. The coolant then passes from the fluid cooler into the radiator bottom hose.
Two quick release connectors on the cooler provide for the attachment of the transmission fluid pipes to and from the transmission. Fluid is supplied from the transmission fluid pump into the lower connection of the cooler. After passing through the cooler, the fluid passes out of the upper connection and is returned to transmission fluid pan.
In hot climate markets an additional transmission fluid to air cooler is located at the front the radiator. For additional information, refer to Transmission Cooling Description
Block Heater - Cold Climate Markets (if fitted)
The block heater is located on the LH (left-hand) side of the engine cylinder block. The heater is located in the oil cooler inlet hose and is secured by a clamp to a threaded hole in the cylinder block which normally locates the support bracket for the oil cooler inlet hose. The clamp is secured by a bolt which screws into a threaded spacer, which in turn is screwed into the cylinder block. The oil cooler inlet hose is secured to the heater inlet and outlet connections with worm drive clamps.
The block heater is available in 2 versions; 115V and 230V dependant on market.
A harness supplied with the block heater kit, connects between the heater and an external socket located in the LH (left-hand) side of the front bumper. The external socket allows the heater to be connected to an external mains power supply.
The block heater is mounted low in the cooling system as the coolant flow of heated engine coolant from the heater is based on the principle of self-circulation by heat convection.
The block heater will maintain the engine coolant at a temperature of between 60 to 80°C (140 to 176°F) ± 5°C (41°F) depending on ambient temperature.
The block heater has 3 connection pins; a mains (115/230 V) power supply, a neutral and a ground. The ground is also connected to the vehicle body near to the external connector plug.