Fault Phenomenon: Caterpillar 950 wheel loader unable to observe hydraulic oil level through the sight glass; the glass interior is cloudy or has oil sludge.

Troubleshooting Process:
– Checked sight glass: glass aged and foggy or oil entered internally.
– Checked seal: sight glass seal aged, allowing moisture or air ingress.
– Checked cleanliness: external dirt buildup.
– Checked oil quality: emulsified oil causing deposits on the glass.

Root Cause: The seal between the sight glass and metal frame failed, allowing oil vapor to enter the glass interior or preventing external dirt from being cleaned.

Required Parts: Replace hydraulic tank sight glass assembly.