This page covers repair and troubleshooting information for the engine cooling system.
Coolant Pump and Thermostat
A centrifugal-type coolant pump is mounted to the front of the engíne. The belt-driven pump circulates coolant through the system whenever the engíne is running. Athermostat controls the flow of coolant into the radiator.When the engíne is cold the thermostat is closed so coolant bypasses the radiator, recirculating from the engíne directly back to the pump. When the engíne reaches operating temperature, thethermostat opens and coolant circulates through the whole system including the radiator .
Radiator and Expansion Tank
The radiator is a crossflow design . A translucent expansion tank provides for coolant expansion at higher temperatures and easy monitoring of the coolant level.
On 4-cylinder models, the radiator expansion tank is integral with the radiator.
On 6-cylinder models, astand alone expansion tank is used.
On cars with automatic transmission, ATF is circulated through an additional heat exchanger (ATF cooler).
Belt-driven cooling fan.
The primary cooling fan is beltdriven. It is mounted to the front of the coolant pump through a fan clutch . The fan clutch is aviscous fluid coupling that controls the speed of the fan based on engine compartment temperature
Electric cooling fan.
Models with M44 engine and standard transmission substitute an electric fan for the belt-driven viscous fan. This is attached to the rear of the radiator and controlled via the DME 5.2 engine management system .
NOTE: The electric cooling fan in these models is activated by the engine control module (ECM).
Auxiliary cooling fan. In all models a two-speed electric auxiliary cooling fan is mounted behind the front grill and in front of the radiator . This fan is primarily used for the A/C system, but also operates when the coolant temperature exceeds a predetermined level.
WARNING -" At normal operating temperature the cooling system is pressurized. Allow the system to cool as long as possible before opening-a minimum of an hour-then release the cap slowly to allow safe release of pressure. Releasing the cooling system pressure lowers the coolants boiling point and the coolant may boíl suddenly. Use heavy gloves and wear eye and lace protection to guard against scalding.
"Use extreme care when draining and disposing of engine coolant. Coolant is poisonous and lethal to humans and pets.
CAUTION-"Avoid adding cold water to the coolant while the engine is hot or overheated. If it is necessary to add coolant to a hot system, do so only with the engine running and coolant pump turning.
Most cooling system faults can be grouped into one of three categories :
" Cooling system leaks
" Poor coolant circulation
" Radiator cooling fan faults
When investigating the cause of overheating or coolant loss, begin with avisual inspection . Be sure to check the condition and tension of the coolant pump drive belt .
•Check hoses for cracks or softness . Check clamps for looseness.
•Check the coolant level and check for evidence of coolant leaks from the engine.
•Check that the radiator fins are not blocked with dirt or debris
.Clean the radiator using low-pressure water or compressed air. Blow outward, from the engine side out.
Inspect the coolant pump by first removing the drive belt from the pump. Firmly grasp opposite sídes of the pulley and check for play in all directions. Spin the pulley and check that the shaft runs smoothly.
NOTE: Thecoolant provides lubrication for the pump shaft, so an occasional drop of coolant leaking from the pump is acceptable. If coolant drips steadily from the vent hole, the pump should be replaced.
The cooling system becomes pressurized at normal operating temperature, which raises the boiling point of the coolant.
Leaks may prevent the system from becoming pressurized, allowing the coolant to boil at a lowertemperature. If visual evidence is inconclusive, a cooling system pressure test can help to pinpoint hard-to-find leaks.
If the cooling system is full of coolant and holds pressure, the next most probable cause of overheating are:
" Faulty radiator fan
" Loose or worn drive belt
" Failed thermostat or coolant pump
" Clogged/plugged radiator or coolant passages .
NOTE -"Some early style coolant pumps were fitted wíth fiberlplastic type impellers . Over time, this impeller can wear away and result in overheating. The plastic impeller can also slip orfree-wheel on the pump shaft. If the engine overheats and no other faults can be found, the old style impeller may be the cause of the problem.
"Only pumps with the updated metal impeller should be used for replacement. Or the new fibre enforced compound version
Cooling System Pressure Test.
A cooling system pressure test is used to check for internal leaks. Some of the common sources of internal leaks are a faulty cylinder head gasket, a cracked cylinder head, or a cracked cylinder block.
To do a cooling system pressure test, a special pressure tester is needed.
At normal operating temperature- the cooling system is pressurized. Allow the system to cool before opening. Release the cap slowly to allow safe retease of pressure.
With the engine cold, install a pressure tester to the expansion tank . Pressurize the system to the specification listed below.
•Pressure should not drop more than 0.1 bar (1 .45 psi) for at least two minutes. If the pressure drops rapidly and there is no sign of an externa¡ leak, the cylinder head gasket may be faulty.
•The screw-on type expansion tank cap should also be tested. using a pressure tester and the correct adapter.
Cooling System Test Pressure
" Radiator test pressure . . . . . . 1 .5 bar (21 .75 psi)
" Radiator cap test pressure . . . . . . . 2 bar (29 psi)