Which of the following are common indicators of hydraulic system contamination?

• A. No visible signs
• B. Leaks, reduced performance, foaming, and erratic pressure readings
• C. Temperature changes only
• D. Sudden complete system failure with no leakage

Answer: (B)

Contamination in a hydraulic system tends to reveal itself through several combined symptoms that reflect degraded fluid quality and altered flow. Leaks often appear as seals and fittings are attacked by abrasive particles, another sign that the fluid isn’t behaving as it should. Reduced performance comes from clogged filters, restricted passages, or worn pump and valve components, all of which slow or weaken system operation. Foaming indicates air or water in the oil, which disrupts lubrication and changes how pressure and flow behave. Erratic pressure readings occur when contaminants cause irregular flow, valve stiction, or air entrainment, leading to unstable or spiky readings. Seeing these indicators together strongly points to contamination rather than a single, isolated issue. If you only notice temperature changes, or no signs at all, or a sudden complete failure with no leakage, those scenarios don’t fit the common contamination pattern, which usually shows multiple observable or measurable symptoms. When these signs appear, testing the fluid, inspecting filters, and checking for particulates and moisture help pinpoint the contamination source and necessary corrective actions.