USCG Exam PracticeDiesel engine principles (motor propulsion)
In a marine diesel's indirect cooling system, what is the primary function of the thermostatic (temperature-regulating) valve?
- A. To regulate seawater flow through the sea suction strainer based on ambient sea temperature
- ✓ To bypass the jacket-water cooler until the engine reaches operating temperature, then progressively admit jacket water to the coolerCorrect
- C. To control the ratio of treated fresh water to seawater admitted to the cylinder jackets
- D. To open a bypass around the lube-oil cooler when jacket-water temperature exceeds the alarm setpoint
Why B is correct
The thermostatic valve bypasses the cooler until the jacket water is warm, then admits it to the cooler as the engine heats up, holding the outlet temperature in a narrow band regardless of load or sea temperature. Running too cold causes incomplete combustion and acidic corrosion; running too hot scores liners and can crack heads.
Cited:NAVEDTRA 14075 §3-5