🔍 Key Concepts

• Study the relative pressures in each pair of fluids: jacket fresh water vs raw (sea) water in the RW/FW heat exchanger, and jacket fresh water vs lube oil in the lube oil cooler. • Trace where each fluid is connected to the expansion tank and which side is vented to atmosphere; this tells you where any leaked fluid can raise or lower the tank level. • Think about which side of each cooler is likely to be at the higher pressure while the engine is running, and therefore which way a leak will actually flow.

💭 Think About

• For a RW/FW heat‑exchanger tube leak, which fluid has the higher operating pressure: the engine jacket fresh water side or the raw water side? Given that, would the leak flow into the FW system (toward the expansion tank) or out to sea? • For a lube oil cooler tube leak, compare normal lube‑oil pressure to jacket‑water pressure. If the higher‑pressure fluid enters the lower‑pressure system, how would that show up in the expansion tank level and in the lube oil sump level? • If fresh water is lost from the closed jacket‑water system, what visible sign do you get at the expansion tank? If fresh water is gained (something else pushing into it), what sign do you get?

✅ Before You Answer

• Be sure which system is closed and vented to the expansion tank (and therefore shows level changes) and which systems discharge overboard. • Verify which side (FW, RW, or LO) is normally at the highest pressure during operation; leaks normally go from higher to lower pressure. • Check that your chosen option is consistent for both components: RW/FW heat exchanger behavior and lube oil cooler behavior must match the same pressure‑direction logic.