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, a stand alone expansion tank is used.

On cars with automatic transmission, ATF is circulated through an additional heat exchanger (ATF cooler).

Cooling Fans

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 a viscous 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.

TROUBLESHOOTING

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 a visual 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: The coolant 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 lower temperature. 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 fiber plastic type impellers . Over time, this impeller can wear away and result in overheating. The plastic impeller can also slip or free-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.

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.
WARNING : 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)

CAUTION
Exceeding the speclfied test pressure could damage the radiator or other system components. Carefully inspect the radiator cap for damage. Replace a faulty cap or a damaged cap gasket .

Part 2:
Thermostat Quick Check
To check if the thermostat is opening and coolant is circulating through the radiator, allow a cold engine to reach operating temperature (temperature gauge needle approximately centered). Shut off engine. Feel the top radiator hose. If the hose is hot to the touch, the coolant is probably circulating correctly. If there are any cool areas in the hose or radiator, coolant flow to the radiator is probably restricted . Check for a faulty thermostat or a plugged radiator.

NOTE: A thermostat that is stuck open will cause the engine to warm up slowly and run below normal Temperature at highway speed. A thermostat that is stuck closed will restrict coolant flow to the radiator and cause overheating . If the engine overheats and no other cooling system tests indicate trouble, the radiator may have some plugged passages that are restricting coolant flow .

Temperature Gauge Quick Check
The coolant temperature sensor is located on the intake manifold (left) side of the cylinder head, under the intake man ifold runners.In early models, the engine coolant temperature (ECT) sensor for the fuel injection and the coolant temperature gauge sender are located side by side .In later models, the ECT sensor and the gauge sender are combined into one sender unit .

RADIATOR AND COOLING SYSTEM
A quick test at the coolant temperature gauge sender can determine if the gauge is functioning correctly. lf the gauge needle remains at the rest position with the engine warm, remove the harness connector from the sender and jumper the correct terminals in the connector to simulate a high engine temperature.
WARNING: 1996 and laten models are OBD 11 compliant. Disconnecting electrical connectors wíth the ignition turned on may set fault codes in the ECM. It is recommended that you leave the diagnosis of faults in the coolant temperature sensorsystem to the BMW dealer service department which has specialized OBD 11 scan tool equipment. If the gauge needle reads too high when the engine is cold, remove the harness connector from the sender. Turn the ignition on. lf the gauge needle position does not change, the wiring or the gauge is shorted to ground. If the gauge needle drops, the sender is faulty and should be replaced . When replacing a faulty coolant temperature sender, the gasket ring on the sender should also be replaced.

Tightening Torque
Temperature gauge sender to engine 18 Nm (13 ft-Ib)

Cooling fan, testing
NOTE: On M44 engines with manual transmission, the primary electric cooling fan is mounted on the engine side of the radiator and is controlled by the engine control module(ECM). Troubleshooting this circuit should be left to anauthorized BMW dealer with the proper diagnostic equipment. An otherwise sound cooling system may still overheat, particularly with prolonged idling, due to a failure of the coolíng fan(s).
The belt-driven cooling fan is controlled by a temperature dependent viscous clutch . A failed fan clutch may affect air flow through the radiator resulting in overheating or possibly overcooling .
With the engine off, check the fan clutch by spinning the fan. The fan should spin on the clutch with some resistance.Check for signs of leaking fluid from the clutch . If the fan freewheels with no resistance, cannot be tu rned by hand, or there are signs of oil leakage, the clutch should be replaced .The auxiliary cooling fan comes on when coolant temperature exceeds a predetermined level or whenever the air conditioning is on. A dual-range temperature switch for cooling fan control is mounted on the right side of the radiator.

WARNING: "Use caution when testing the electric cooling fan(s) and coolant temperature switch . Keep hands andwires clear ofthe fan blades. The cooling fan(s) can run any time the ignition is ON. "For greatest safety, coolíng fan and coolant temperature switch tests should be performed on a cold engine with the air conditioning off.

If a faulty thermostat, trapped air, or a restriction in the system is not allowing the coolant to circulate through the radiator, the temperature switch will not close and the auxiliary cooling fan will not run. Before making the tests described below, make sure the thermostat is operating correctly as described earlier. The normal switching temperatures for the dual -speed switch

Auxiliary Cooling Fan Switching Temperatures - speed Switching temperature
Low speed 196°F(91°C)
High speed 210°F(99°C)

NOTE: Some cars covered by this manual may have an alternate cooling fan switch with switching temperatures of 176%190W (80%88°C). When replacing the switch check the switching specifications, which should be stamped on the switch body.
1 . If coolant is circulating at normal operating temperature, but auxiliary cooling fan does not run, disconnect connector from radiator temperature switch and make tests
2. If fan runs only when powered directly by jumpered connector and hot coolant is circulating through radiator, radiator temperature switch is most likely faulty. Usea new sealing ring when replacing switch.

Tightening Torque: Temperature switch to radiator . 15 Nm (11 ft-Ib)

3. If auxiliary fan does not run when powered directly, check for battery voltage at temperature switch connector (black/green wire) with ignition on . If battery voltage is not present, check fuses.

Auxiliary Cooling Fan Circuit Fuses
Fuse16 . . . . . . . . . . . . . . . . . . . . .5 amp
Fuse 41 (ex. M44 w/man. trans) . . . . . . . 30 amp
Fuse 48 (M44 w/man. trans. only) . . . . . . 40 amp

4. If no faults are found, remove low speed relay and turn Coolant, draining and filling ignition ON. "Check for power at terminal 30 and terminal 86 of relay socket. "Reinstall low speed relay and repeat test at high speed relay socket . Fix any wiring faults found. On early production cars (up to 9/92): If fan operates only on high speed and no electrical faults have been found up to this point, use an ohmmeter to check that fan resistor is not electrically open. Resistor is mounted on auxiliary cooling fan housing behind front grille .

COOLING SYSTEM SERVICE

Coolant, draining and filling
1 . Remove expansion tank cap. Set temperature controls to full warm. WARNING - Allow the cooling system to cool before opening or draining the cooling system.
2. Place 3 gallon pail beneath radiator drain plug and remove drain plug.

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