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Heavy Duty Equipment Technician Red Seal Exam Prep · Question

An off-road grader's hydrostatic drive system is experiencing intermittent loss of power. Oil samples from the hydraulic system consistently show a significant increase in ferrous wear particles (iron, Fe) and minor amounts of chromium (Cr), along with a sharp drop in viscosity compared to new oil. What is the most probable cause?

A sharp drop in viscosity combined with ferrous wear indicates severe oil degradation, most often caused by excessive operating temperatures. This high temperat

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Question: An off-road grader's hydrostatic drive system is experiencing intermittent loss of power. Oil samples from the hydraulic system consistently show a significant increase in ferrous wear particles (iron, Fe) and minor amounts of chromium (Cr), along with a sharp drop in viscosity compared to new oil. What is the most probable cause?

Answer options: ✅ Excessive operating temperature degrading the hydraulic fluid.

  • Ingress of fine metallic debris from external sources.
  • Internal pump or motor wear leading to cavitation.
  • Contamination from a water leak in the system.

Correct answer: Excessive operating temperature degrading the hydraulic fluid.

Explanation: A sharp drop in viscosity combined with ferrous wear indicates severe oil degradation, most often caused by excessive operating temperatures. This high temperature causes the oil to thin, accelerating wear (Fe and Cr from hardened steel components) and reducing its lubricating effectiveness. All other options do not fully explain BOTH the viscosity drop and specific wear metal combination as a primary cause.

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