Which action is required when hydraulic fluid has been contaminated by an incompatible fluid?

• A. Inspect for contamination
• B. Drain and flush the system
• C. Replace seals
• D. Refill with compatible fluid

Answer: (B)

When hydraulic fluid is contaminated with an incompatible fluid, the essential action is to physically remove the contaminant by draining and flushing the system. Incompatible fluids can react with the hydraulic oil, degrade seals and elastomers, form varnish or sludge, and clog valves and routes. Simply inspecting for contamination won’t remove the contaminant or stop ongoing damage, and refilling with clean fluid without flushing would recycle the problem back into the system. Draining removes the old, contaminated fluid, flushing with clean, compatible fluid cleans passages and components, and then you refill with the correct fluid, replace filters, and inspect for any damage (seals or components may need replacement if deterioration is found).