- Joined
- Feb 18, 2016
- Points
- 231
- Model of Z
- Z3M Imola and Z4 (e89)
Thought this may be helpful to some.
Viscous Fans Explained
Viscous fan couplings are used on vehicles (cars and trucks) with inline engine positions, mainly rear wheel drives. These fans are needed at slow speeds and while idling. A faulty fan can cause an engine to overheat while idling or in heavy traffic, or poor mileage and loss of horse power.
Location
Viscous fan couplings are located between the water pump pulley and the radiator.
Function
• Controls fan speeds to aid engine cooling
• Aids in the efficiency of the engine by engaging the fan, when necessary
• Reduces load on the engine
Assembly
Either assembled directly to a flanged shaft mounted onto the pulley of the water pump, or alternatively it can be threaded directly to the water pump hub.
The Mechanism
This product is based on the bimetal sensor located at the front of the viscous fan. This sensor expands or contracts, depending on the temperature imparted through the radiator. This intelligent component improves engine efficiency by regulating the RPM of the engine fan and cool air supply.
At Cold Temperatures
The bimetal sensor contracts closing the valve, so the silicone fluid remains in the reservoir chamber. At this stage, the viscous fan coupling is disengaged and turns at around 20% of the rotation speed of the engine.
At Operating Temperatures
The bimetal sensor expands, rotating the valve and allowing the silicone fluid to move through the entire chamber to the outer edges. This generates enough torque to drive the cooling fan blades at engine operating speeds and remain at a consistent temperature. At this stage, the viscous fan coupling is engaged and turns at around 80% of the rotation speed of the engine.
Failure
It is good practice to always check the condition of the viscous fan coupling when the water pump is replaced. A worn coupling will directly affect the water pump’s lifespan. A failed viscous fan coupling can stay stuck in the engagement position meaning it will always run at 80% of the engine rotation speed. This can cause disruption with high noise and vibration, making a loud whirling sound as the engine is revved and will increase fuel consumption.
On the other hand, if the viscous fan coupling fails in the disengaged position, it will not draw air through the radiator. This in turn will lead to the engine overheating as the cooling process is disrupted.
Common Causes of Failure
• Leaking silicone fluid, disengaging the fan coupling.
• Bimetal sensor losing its properties due to surface oxidation, causing the coupling to be stuck disengaged.
• Bearing failure, although uncommon can occur if the viscous fan coupling has not been replaced after high mileage. This results in the condition of the blades deteriorating.
Understanding the Sensor
The bimetal sensor governs the functioning of the viscous fan coupling. Primarily, there are two kinds of bimetal sensor systems: plate and coil. Both of them work under the same principle, as explained previously.
The only difference is that whilst the coil expands and contracts to turn the rotation plate, the bimetal contracts and bends. This moves the slide plate and allows the silicone fluid to move from the reservoir chamber to the cavity.
Viscous Fans Explained
Viscous fan couplings are used on vehicles (cars and trucks) with inline engine positions, mainly rear wheel drives. These fans are needed at slow speeds and while idling. A faulty fan can cause an engine to overheat while idling or in heavy traffic, or poor mileage and loss of horse power.
Location
Viscous fan couplings are located between the water pump pulley and the radiator.
Function
• Controls fan speeds to aid engine cooling
• Aids in the efficiency of the engine by engaging the fan, when necessary
• Reduces load on the engine
Assembly
Either assembled directly to a flanged shaft mounted onto the pulley of the water pump, or alternatively it can be threaded directly to the water pump hub.
The Mechanism
This product is based on the bimetal sensor located at the front of the viscous fan. This sensor expands or contracts, depending on the temperature imparted through the radiator. This intelligent component improves engine efficiency by regulating the RPM of the engine fan and cool air supply.
At Cold Temperatures
The bimetal sensor contracts closing the valve, so the silicone fluid remains in the reservoir chamber. At this stage, the viscous fan coupling is disengaged and turns at around 20% of the rotation speed of the engine.
At Operating Temperatures
The bimetal sensor expands, rotating the valve and allowing the silicone fluid to move through the entire chamber to the outer edges. This generates enough torque to drive the cooling fan blades at engine operating speeds and remain at a consistent temperature. At this stage, the viscous fan coupling is engaged and turns at around 80% of the rotation speed of the engine.
Failure
It is good practice to always check the condition of the viscous fan coupling when the water pump is replaced. A worn coupling will directly affect the water pump’s lifespan. A failed viscous fan coupling can stay stuck in the engagement position meaning it will always run at 80% of the engine rotation speed. This can cause disruption with high noise and vibration, making a loud whirling sound as the engine is revved and will increase fuel consumption.
On the other hand, if the viscous fan coupling fails in the disengaged position, it will not draw air through the radiator. This in turn will lead to the engine overheating as the cooling process is disrupted.
Common Causes of Failure
• Leaking silicone fluid, disengaging the fan coupling.
• Bimetal sensor losing its properties due to surface oxidation, causing the coupling to be stuck disengaged.
• Bearing failure, although uncommon can occur if the viscous fan coupling has not been replaced after high mileage. This results in the condition of the blades deteriorating.
Understanding the Sensor
The bimetal sensor governs the functioning of the viscous fan coupling. Primarily, there are two kinds of bimetal sensor systems: plate and coil. Both of them work under the same principle, as explained previously.
The only difference is that whilst the coil expands and contracts to turn the rotation plate, the bimetal contracts and bends. This moves the slide plate and allows the silicone fluid to move from the reservoir chamber to the cavity.