What discoloration may indicate finely divided rust particles when evaluating an oil sample for water presence?

What discoloration may indicate finely divided rust particles when evaluating an oil sample for water presence?

• A. Muddy, reddish brown
• B. Bright yellow
• C. Clear and colorless
• D. Blue-green

Answer: (A)

When oil is contaminated with water, iron parts in the machine can begin to rust. Finely divided rust particles that form are iron oxide, and when they stay suspended in oil they scatter light in a way that gives the oil a muddy, reddish-brown hue. That color change is a sign that water is present and corrosion is occurring, which is why muddy, reddish-brown discoloration is the best indicator of finely divided rust particles in an oil sample. Other colors don’t point to rust: bright yellow can be varnish or certain oxidation by‑products, clear and colorless means the oil is clean, and blue-green suggests copper or alloy corrosion rather than iron oxide rust.

When oil is contaminated with water, iron parts in the machine can begin to rust. Finely divided rust particles that form are iron oxide, and when they stay suspended in oil they scatter light in a way that gives the oil a muddy, reddish-brown hue. That color change is a sign that water is present and corrosion is occurring, which is why muddy, reddish-brown discoloration is the best indicator of finely divided rust particles in an oil sample. Other colors don’t point to rust: bright yellow can be varnish or certain oxidation by‑products, clear and colorless means the oil is clean, and blue-green suggests copper or alloy corrosion rather than iron oxide rust.