BMW E46 cooling system components include:
- Radiator and coolant overflow tank.
- Belt driven coolant pump bolted to the front of the engine block.
- Electric cooling fan attached to rear of radiator. The cooling fan is controlled by the engine control module (ECM) via an output final stage.
- Automatic transmission models: Belt driven fan attached to front of coolant pump. Viscous clutch controls fan speed based on engine temperature and rpms.
- Electrically heated thermostat.
- Automatic transmission cooler (heat exchanger).
- Heater valve and heater core (for climate control).
- Coolant level sensor inside expansion tank.
- Coolant temperature sensor at cylinder head.
- Radiator outlet temperature sensor
- Coolant hose and lines.
A viscous fan clutch is as reliable as any other part of your cooling system, but it can still fail. The viscous fan clutch is mounted between the radiator and engine. The clutch controls radiator cooling fan speed and is dependent on engine temperature. The fan draws air through the radiator cooling fins, thus cooling the engine coolant. Depending on cooling needs, the fan clutch partially disengages the fan, located at the front of the water pump and driven by the engine drive belt. Disengaging the fan when not required saves power, since the engine does not have to fully drive the fan. However, if engine temperature rises above 90° C (194°F), the fan becomes fully engaged, drawing a higher volume of air through the radiator cooling fins.
A common symptom of viscous fan clutch failure is engine overheating at idle or in traffic because the viscous fluid in the clutch has dried up or failed in some way. On the other hand, if a viscous fan clutch is stuck ON, it will rob your engine's power and decrease fuel economy. Another potential symptom of your fan clutch being stuck ON in a cold weather climate is that the heating system doesn't deliver sufficient hot air. The bearings in the fan clutch can also fail, causing a noise or fan blades to come in contact with the fan shroud.
In this tech article, I will go over how to test the fan clutch a few different ways.
Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.
Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.
Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.
This photo shows the fan clutch, installed on the cooling fan (green arrow).
Clutch bearing free-play
Check bearing free-play by wiggling fan back and forth. Tilt play of bearing with diameter 120 mm is ± 0.65 mm If free-play is more than specified amount, replace with new. Spin test With engine cool and OFF, spin fan blades by hand. If the fan free-wheels without drag (the fan blades will revolve more than five turns when spun), replace the fan clutch.
Use extreme caution when the engine is running. Do not stand in line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator (or air conditioner condenser). Use tape at the top to secure the plastic and be sure that the air flow is blocked. Be sure that A/C is turned OFF.
Start the engine and raise idle to 2400 RPM. Within ten minutes the air temperature should be up to 88°C (190°F). Fan clutch engagement should have started to occur between 88°to 90°C (190°to 194°F). Engagement is distinguishable by a definite increase in fan flow noise (roaring). Fan speed will increase. Use an infrared temperature gun to measure fan clutch temperature.
When the air temperature reaches 88°C (190°F), remove the plastic sheet. Fan clutch disengagement should start to occur at 60°to 79°C (140°). A definite decrease of fan flow noise (roaring) should be noticed. If not, replace the defective viscous fan clutch.