USCG Exam PracticeDiesel engine principles (motor propulsion)
In a marine diesel indirect cooling system, what is the purpose of the thermostatic (temperature-regulating) valve?
- A. It controls the flow of treated fresh water through the lube-oil cooler to prevent overheating of the lubricating oil.
- ✓ It bypasses the heat exchanger until jacket water reaches operating temperature, then progressively admits jacket water to the cooler.Correct
- C. It regulates seawater flow through the strainer to prevent cavitation in the raw-water pump.
- D. It vents air from the closed jacket-water loop to maintain system pressure.
Why B is correct
NAVEDTRA 14075 §3-5 describes the thermostatic valve as bypassing the cooler until the jacket water is warm, then admitting it to the cooler as the engine heats up, holding outlet temperature in a narrow band regardless of load or sea temperature. This prevents both the damage of running too cold and the damage of running too hot.
Cited:NAVEDTRA 14075 §3-5