When shifting heat exchangers such as main engine lube-oil coolers, what statement represents the recommended operating procedure if the shift is to occur during engine operation?

Correct Answer: Option C — First, introduce cooling water to the on-coming cooler, then introduce lube oil to the on-coming cooler. Next, secure lube oil to the off-going cooler, then secure cooling water to the off-going cooler.

Introducing cooling water to the oncoming cooler first ensures it is ready to absorb heat. Once the cooling medium is established, introducing the lube oil allows for a smooth transition. Securing the off-going unit in reverse order prevents thermal shock and ensures the engine remains protected throughout the shift.