🔍 Key Concepts

• Lube oil system flow path: pump → bearings → drain to sump → return to tank • How a sight glass indicates normal flow vs. backed-up oil • Effect of drain restrictions vs. air or temperature changes on oil level/flow

💭 Think About

• Think about what would physically make the oil level rise high enough to completely cover the sight glass instead of showing a thin moving stream. • Which condition would cause oil to back up at the bearing instead of draining freely to the sump? • For each option, ask yourself: does this change the amount of oil flowing past the glass, or does it change how easily the oil can leave that area?

✅ Before You Answer

• Identify what a normal sight glass should look like in a main bearing lube system (stream/half-full vs. full). • Decide which options would increase backpressure or resistance in the drain side of the system. • Eliminate options that mainly affect temperature or air content without directly blocking the oil’s ability to drain away from the bearing.