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Heavy Duty Equipment Technician Red Seal Exam Prep · Question

During a routine service on a forestry feller buncher, the technician notices that the primary fuel filter is significantly clogged with dark, slimy residue, despite having been replaced just 100 hours ago (manufacturer's interval is 500 hours). The machine is stored outdoors. What is the most likely cause for the premature filter clogging?

Dark, slimy residue in fuel filters, especially when encountered prematurely and on equipment stored outdoors, is a classic sign of microbial contamination, com

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Question: During a routine service on a forestry feller buncher, the technician notices that the primary fuel filter is significantly clogged with dark, slimy residue, despite having been replaced just 100 hours ago (manufacturer's interval is 500 hours). The machine is stored outdoors. What is the most likely cause for the premature filter clogging?

Answer options:

  • Over-tightening of the fuel filter during installation.
  • Fuel pump malfunction causing excessive cavitation. ✅ Microbial growth (diesel bug) in the fuel tank.
  • Using a fuel filter with an incorrect micron rating.

Correct answer: Microbial growth (diesel bug) in the fuel tank.

Explanation: Dark, slimy residue in fuel filters, especially when encountered prematurely and on equipment stored outdoors, is a classic sign of microbial contamination, commonly known as 'diesel bug'. This growth thrives in the presence of water in fuel tanks.

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