BMW 850Ci Radiator Fan Isn't Working

Diagnosing the Causes of a Non-Functioning Radiator Fan in Your BMW 850Ci and How to Fix It

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Reviewed by
Andrew Hajjar
Written by RepairPal Car Genius
Updated January 14, 2025
0%
34% chance it's the
Fan Motor or Clutch
0%
28% chance it's the
Fan Relay or Fuse
0%
23% chance it's the
Temp Sensor or Fan Control Module
0%
15% chance it's
Something else
The most common reasons a BMW 850Ci radiator fan isn't working are the fan assembly, the fan clutch, or the coolant temperature sensor.
  • Fan Motor or Clutch: A faulty fan motor or a malfunctioning fan clutch can result in inadequate cooling, causing the engine to overheat.
  • Fan Relay or Fuse: A faulty fan relay or blown fuse can prevent the cooling fan from operating, leading to engine overheating.
  • Temp Sensor or Fan Control Module: A faulty temperature sensor or fan control module can result in incorrect readings, causing the engine to overheat or the cooling fan to operate improperly.
Proper diagnosis will determine the exact cause of your symptom, saving you money on unnecessary repairs. The diagnostic experts at RepairPal Certified shops have the right tools and experience to solve any symptom.

How much does it cost to fix a BMW 850Ci radiator fan isn't working?

Common Repairs

The total repair cost will vary based on the condition of your vehicle and the number of repairs needed to fix your symptom. Proper diagnosis will save you money by finding the exact repairs needed to fix your car right the first time.

Over time serpentine belts stretch, crack, and the ribs that ride on the accessory pulleys being to wear smooth. A squealing noise that increases with engine speed or as engine driven accessories are turned on may be noted. The noise is caused by the belt slipping on the pulleys, insufficiently driving them. Ineffective air conditioning, a battery warning light, or intermittent power steering assist can result from this.

»MORE: Symptoms of a bad serpentine belt

The first indication of a defective fan clutch is a healthy cooling system that runs below or above the normal temperature range. This is due to the fan running too fast or too slow. Also, a seized cooling fan will cause a loud roaring fan noise from under the hood every time the accelerator is pressed, and the engine will feel as if it lacks power. In this situation it would be very difficult to turn the engine cooling fan by hand, of course when the vehicle is off. Finally, if the clutch fails the fan will either turn very slowly, and not respond well to engine speed.

The bad thermostat can cause two different sets of problems, depending on whether it's stuck open or stuck closed.

A thermostat that is stuck open can cause the engine to run colder than normal and turn on the check engine light. It may also cause poor fuel mileage and the heater to blow cool air.

A thermostat that is stuck closed will cause the vehicle to overheat. If a new thermostat doesn't resolve engine temperature problems, the cooling system needs to be checked for other issues.

» LEARN MORE: Signs of a bad thermostat, and how to fix it

When the engine coolant temperature sensor fails, it will send inaccurate information to the vehicle’s computer, causing the computer to react to false operating conditions. This will cause the engine to consume more fuel than normal, depleting fuel mileage, and causing black, sooty smoke from the engine under moderate to heavy acceleration. The check engine light will illuminate, and on-board diagnostic trouble codes may be stored for exhaust and emission system failure, fuel delivery system failure, and engine cooling system failure. Overheating may also occur, as the coolant sensor may be leaking fluid out of the engine, creating a an air pocket in the system.

Troubleshooting Radiator Fan Issues in a BMW 850Ci

When troubleshooting radiator fan issues in a BMW 850Ci, it's crucial to adopt a systematic diagnostic approach. Begin with the simplest solution by checking the fuse associated with the fan; a blown fuse can often be the culprit and is easy to replace. If the fuse is intact, inspect the fan itself for any visible damage or wear, as a malfunctioning fan may need replacement. To further assess the fan's functionality, consider hotwiring it to see if it operates independently, which can help pinpoint whether the problem lies with the fan, a relay, or the fuse. Additionally, don't overlook the viscous fan connected to the water pump, as issues here can also affect performance. Lastly, be aware of common problems reported by other BMW 850Ci owners, such as brake squeal, which may indicate broader electrical or mechanical issues. By following this structured approach, you can effectively diagnose and address radiator fan problems, ensuring your vehicle runs smoothly.

What to Check When the Radiator Fan Isn't Working in a BMW 850Ci?

When troubleshooting a non-functioning radiator fan in a BMW 850Ci, it's essential to consider several common problems that could be at play. Start by examining the fan assembly itself, as a faulty unit can prevent the fan from operating effectively. Next, check the fan clutch, which is responsible for engaging the fan when needed; if it's malfunctioning, the fan may not spin as required. Additionally, the coolant temperature sensor is critical for regulating fan operation; a defective sensor can lead to incorrect readings, causing the fan to remain inactive. Lastly, inspect the viscous fan, which relies on the main belt from the crankshaft pulley for engagement; if it fails to engage properly, the cooling system will not function as intended. By systematically checking these components, you can identify the root cause of the issue and take appropriate action to restore your BMW 850Ci's cooling efficiency.

Why is it Critical to Fix a Non-Working Radiator Fan in a BMW 850Ci?

A non-working radiator fan in a BMW 850Ci is not just a minor inconvenience; it poses serious risks that require immediate attention. The radiator fan is essential for regulating engine temperature, and when it fails, the engine can quickly overheat. This overheating can lead to catastrophic engine damage, resulting in costly repairs that could have been avoided with timely intervention. Additionally, a malfunctioning fan can compromise the vehicle's air conditioning system, making it difficult to maintain a comfortable cabin temperature, especially during hot weather. Ignoring the signs of a failing radiator fan can lead to decreased engine efficiency and performance, ultimately jeopardizing the longevity of your vehicle. Therefore, addressing any issues with the radiator fan promptly is crucial to ensure the safety, comfort, and reliability of your BMW 850Ci.

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