USCG Exam PracticeDiesel engine principles (motor propulsion)
In a marine diesel indirect cooling system, what is the primary purpose of the thermostatic (temperature-regulating) valve?
- A. To control the flow of treated fresh water into the expansion tank
- ✓ To bypass the jacket-water cooler until the engine reaches operating temperature, then admit jacket water to the cooler to hold outlet temperature in a narrow bandCorrect
- C. To regulate seawater flow through the sea suction strainer based on engine load
- D. To divert jacket water through the lube-oil cooler when oil temperature exceeds a set point
Why B is correct
NAVEDTRA 14075 §3-5 describes the thermostatic valve as bypassing the cooler until 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 overcooling and overheating.
Cited:NAVEDTRA 14075 §3-5