Engine cooling system
The cooling system serves to maintain the engine's operating temperature.
The heat generated in the engine is absorbed by the coolant flowing through the channels in the cylinder block and cylinder head. This heat is then removed from the coolant by the air as it passes through the radiator.
The coolant enters the water pump, located beneath the front timing gear cover and generating pressure in the cooling system, and passes into the openings in the upper cavity of the cylinder block and in the cylinder head gasket. These are formed around each cylinder and between the cylinders.
The coolant enters the cylinder head, flowing around the valve bridge and injector seats. It then passes to the exhaust channels in the cylinder head via the accessory connection points and into the thermostat housing.
Until the engine warms up to the thermostat opening temperature, coolant is fed through the bypass pipe to the water pump inlet. As soon as the engine reaches the opening temperature, the thermostat opens and coolant begins to flow through the radiator, while the bypass channel to the water pump is closed. The thermostat maintains the temperature within the range of 82–95 °C.
Main components of the cooling system
Radiator
The radiator has a tubular-and-strip core and tanks made of polymer material. The right-hand tank has a plugged hole for draining the coolant.
Expansion tank
An expansion tank is fitted to compensate for changes in coolant volume with temperature. Level marks are provided on the tank body. The tank cap has a relief valve that maintains excess pressure in the system, allowing the coolant to begin boiling only at up to 120 °C.
Water pump
The water pump is mounted on the front cover of the cylinder block and is driven by the accessory drive belt.
Thermostat
The thermostat is installed in a housing secured to the cylinder block. It is closed up to 82 °C and opens at 95 °C.
Fan with viscous coupling
The fan with a plastic impeller is mounted on the front cover of the viscous coupling and secured with four bolts. The fluid-friction fan coupling (viscous coupling) is mounted on a support and secured with a threaded bush.
The fluid-friction coupling allows the fan speed to vary according to the temperature of the air flowing through the radiator: at low temperature the fan speed is minimal, and as the temperature rises it increases. The coupling rotor is not rigidly connected to the housing carrying the fan; torque is transmitted by the internal friction of the working fluid. The fan speed changes as fluid flows between the internal cavities of the coupling, depending on the opening or closing of the internal channels, which is controlled by the movement of a plate valve. The valve position changes with temperature under the action of a bimetallic spring mounted externally at the front of the coupling.
The speed of the fan mounted on the viscous coupling housing increases as the air temperature rises and becomes equal to the engine crankshaft speed. A failed fluid-friction fan coupling can cause engine overheating, especially in difficult road conditions or in traffic jams.
To check the coupling with the engine stopped, verify that the fan turns freely, that there is no significant axial or radial play, and that there are no oil traces. If oil traces are present, the coupling must be replaced. With the engine warm (bonnet closed), set the crankshaft speed to approximately 3000 min⁻¹. The impeller will then rotate slowly due to the residual torque. At a coolant temperature of 80–85 °C the coupling should engage and the fan speed should increase markedly (usually noticeable from the increased noise).
Pre-heater/auxiliary heater
The pre-heater/auxiliary heater is installed in the right-hand cavity of the front bumper (on vehicles in the “Comfort-2” trim). Owing to the design features of the diesel engine, during prolonged idling (especially in cold weather) the coolant temperature gradually falls below normal, which among other things reduces heater performance. The auxiliary heater eliminates this drawback and at the same time performs the function of a pre-heater. The unit runs on diesel fuel supplied from the fuel tank by a special metering pump.
The metering pump is mounted on the inner side of the vehicle frame and connected to the fuel tank and the heater combustion chamber by special plastic fuel lines.
Checking the cooling system connections for leaks
Check for coolant in the expansion tank, the radiator inlet and outlet hoses, and the hose attachment points at the water pump, thermostat, heater valve, heater return pipes, EGR heat exchanger supply and heater supply.
If a leak is noticed, the hose must be removed. The cause of hose leaks is usually corrosion of the sealing surface of the pipes. Clean the area and apply sealant before refitting the hose.
Possible cooling system faults
Materials used: radiator — aluminium tubular-and-strip core with polymer tanks; hoses — oil-resistant rubber with reinforcing braid; seals — heat-resistant rubber; coolant — ethylene glycol-based antifreeze with an additive package (concentration controlled).
Coolant leaks
External coolant leaks
Make sure there are no coolant leaks from hoses, drain taps, the water manifold, connecting pipes, compensation plugs and pipe plugs, fittings, supply and return lines, EGR cooling system venting, turbocharger supply and return lines, EGR valve supply and return lines, EGR cooler and valve, radiator heat-exchange element, compressor and cylinder head gaskets, oil cooler, water pump seal, and components supplied by the equipment manufacturer connected to the cooling system. If necessary, pressure-test the cooling system.
Expansion tank cap incorrectly selected or rated for too low a pressure
Check or replace the expansion tank cap.
Deformation, blockage or lack of sealing of a cooling system hose
Check the hoses.
Blocked, obstructed or incorrectly routed coolant supply or air vent lines
Check the routing of the coolant supply lines and that they are not blocked.
Air entering the cooling system
Make sure there is no air or combustion products in the cooling system.
Gradual or sudden coolant overheating
Active electronic fault codes or a large number of passive fault codes
Read the fault codes and carry out diagnostics using the INSITE kit.
Winter cover or radiator front blind closed
Open the winter cover or radiator front blind.
Radiator fins damaged or blocked
Check the radiator fins.
Coolant level below normal
Check the coolant level and for leaks.
Antifreeze concentration out of specification
Check the antifreeze concentration. Add antifreeze or water to bring it to specification.
Fan shroud or air recirculation baffles damaged or missing
Check the fan shroud and baffles.
Fan drive belt damaged or insufficiently tensioned
Check the fan belt; replace if necessary.
Fan drive or fan control system faulty
Check the fan drive and control system.
Coolant temperature gauge or sensor faulty
Check the gauge and sensor; repair or replace if necessary.
Expansion tank cap valve not working correctly
Check or replace the expansion tank cap.
Thermostat incorrectly selected or faulty
Check the thermostat against the catalogue and check its operation.
Dirt, scale or sediment in the cooling system
Clean the cooling system.
Coolant contaminated with oil
Check for oil entering the cooling system and replace the coolant.
Water pump faulty
Check the pressure in the cylinder block; replace the water pump if necessary.
Coolant temperature below normal
Thermostat incorrectly selected or faulty
Check the thermostat against the catalogue and check its operation.
Fan drive or fan control system faulty
Check the fan drive and control system.
Engine idling for too long
Do not leave the engine idling for prolonged periods.
Coolant in the oil
Oil cooler faulty
Check the oil cooler.
Internal coolant leaks
Pressure-test the cooling system and look for internal coolant leaks.
Cylinder head gasket leaking
Check the cylinder head gasket.
Cracks or porosity in the cylinder head
Pressure-test the cylinder head.
Cracks or porosity in the cylinder block
Check the cylinder block.
