Heavy Duty Equipment Technician Red Seal Exam Prep · Question
A hydraulic excavator's fuel filter is replaced as per the 500-hour PM schedule. Upon cutting open the old filter, the technician observes a significant amount of black, slimy residue. The excavator operates on diesel purchased from a reputable supplier. What is the most likely issue indicated by this finding?
Black, slimy residue found in a fuel filter is a classic indicator of microbial contamination (bacteria or fungi) in the diesel fuel. These organisms thrive in
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Question: A hydraulic excavator's fuel filter is replaced as per the 500-hour PM schedule. Upon cutting open the old filter, the technician observes a significant amount of black, slimy residue. The excavator operates on diesel purchased from a reputable supplier. What is the most likely issue indicated by this finding?
Answer options:
- Normal operation byproduct; no further action needed.
- Excessive engine blow-by contaminating the fuel. ✅ Bacterial or fungal growth in the fuel system.
- Rust and corrosion from water contamination in the fuel tank.
Correct answer: Bacterial or fungal growth in the fuel system.
Explanation: Black, slimy residue found in a fuel filter is a classic indicator of microbial contamination (bacteria or fungi) in the diesel fuel. These organisms thrive in the presence of water and fuel, forming sludge that can clog filters and fuel lines.
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