🔍 Key Concepts

• Purpose of the stern tube lube oil head tank (what is the tank trying to maintain at the seal and bearing) • Relationship between leaks and tank level (where could the oil be going or what could be displacing it) • Difference between temperature effects and loss of fluid in a closed system

💭 Think About

• Ask yourself: In a normally tight stern tube system, would a change in temperature alone make the oil level in the head tank permanently drop, or just expand/contract within the system? • Consider which options would allow lube oil to physically leave the system or be displaced by another fluid so that the head tank has to drain to make up the loss. • Think about where the stern tube seals are located and what fluid is on each side (sea water vs. lube oil). Which condition would let sea water move in or oil move out?

✅ Before You Answer

• Identify which choices involve actual loss of oil or displacement by seawater, not just a change in operating condition. • Confirm that the head tank level only decreases if it is supplying oil to replace a leak somewhere in the system. • Eliminate any options where the effect would mainly be temperature‑related expansion/contraction rather than a net loss of oil.