Would you recognise the symptoms of a faulty viscous clutch before it causes a major failure?

June 15, 2026

In most cases, detecting a viscous clutch failure is not as simple as it sounds.

The problem usually appears progressively: the cooling system continues to function apparently normally, but it gradually becomes less efficient until the vehicle is operating under demanding conditions. That is when abnormal rises in temperature, loss of performance or irregular fan behaviour start to appear. 

In addition, many of these signals can easily be mistaken for other cooling system problems, such as accumulated dirt in the radiator, high ambient temperatures, electronic failures or even problems with other auxiliary components.

Some of the most common symptoms are:

• Fan running constantly

• Fan not engaging or not reaching target speed

• Unexpected noises

• Vibrations in the fan area

• Intermittent overheating of the vehicle

• Loss of cooling efficiency

• Increase in fuel consumption

In many cases, the vehicle does not show problems during normal journeys and the anomalies only appear after several hours of work, prolonged slopes or situations of high thermal load.

Therefore, in applications such as heavy-duty transport, agriculture, construction or industrial machinery, the behaviour of the viscous clutch is key to ensure the thermal stability of the system.

At Cojali Parts we work on these components paying special attention to aspects such as the balancing, the functional response of the coupling or the thermal behaviour under real operating conditions, factors that directly influence the reliability of the cooling system.