What are the long-term effects of using a hydraulic fluid with a lower-than-specified viscosity?

Using a hydraulic fluid with a lower-than-specified viscosity has several negative long-term effects on a hydraulic system, primarily due to increased internal leakage and reduced lubrication. Viscosity refers to a fluid's resistance to flow; a lower viscosity fluid flows more easily. Hydraulic systems rely on the fluid's viscosity to create a seal between moving parts, such as pistons and cylinder bores, or valve spools and valve bodies. A fluid with insufficient viscosity will leak more readily through these clearances, leading to reduced system efficiency and slower operation. This internal leakage reduces the pressure that can be delivered to the actuator, such as a hydraulic cylinder or motor, resulting in decreased force or speed. Lower viscosity also reduces the fluid's ability to maintain a lubricating film between moving parts. This increases friction and wear, especially in high-speed or high-load components like pumps and motors. Increased wear leads to premature component failure and reduced system lifespan. Over time, the wear particles generated can contaminate the hydraulic fluid, further accelerating wear and causing damage to seals and other components. Furthermore, a lower viscosity fluid is more susceptible to temperature-induced viscosity changes. As the fluid heats up, its viscosity decreases further, exacerbating leakage and wear problems. This can lead to inconsistent system performance, especially in applications with varying operating temperatures. For instance, if a hydraulic excavator uses a fluid with too low viscosity, the hydraulic pump may wear out quickly, and the machine's digging force may be significantly reduced, leading to costly repairs and downtime.