Cooling Water Systems Jacket Cooling Water and Piston Cooling Water.

Cooling Water Systems: Jacket Cooling Water and Piston Cooling Water


Cooling systems play a vital role in maintaining optimal operating conditions for marine engines. This article focuses on two essential cooling water systems: the jacket cooling water system and the piston cooling water system. We will explore their functions, components, and the importance of chemical treatment in preventing corrosion and scale formation. Additionally, we will discuss the fuel oil supply system as a crucial part of engine operations.

Jacket Cooling Water System:

The jacket cooling water system utilizes fresh water as a coolant, which circulates through internal passages within the engine. However, to prevent corrosive action and scale formation in the narrow cooling passages, fresh water is cooled by seawater in a cooler. This system ensures that the engine metal retains its mechanical properties and operates within safe temperature limits.

Piston Cooling Water System:

Similar to the jacket cooling water system, the piston cooling water system employs fresh water as a coolant. In some cases, lubricating oil may also serve as the coolant for this system. Proper cooling of the piston helps maintain its integrity and prevents excessive thermal stress during engine operation.

Fuel Oil System:

A large diesel engine’s fuel oil system comprises two primary systems: the fuel oil supply system and the fuel oil injection system. The fuel oil supply system involves the transfer of fuel oil from bunker/storage tanks to the main engine fuel pumps. The process includes settling tanks for water separation, purifiers for removing impurities, and booster pumps for fuel oil delivery to the main engine fuel pumps.

Importance of Chemical Treatment for Cooling Water Systems:

Chemical treatment is crucial to maintain the integrity and efficiency of cooling water systems. Distilled water, used as cooling water, tends to absorb carbon dioxide from the air, becoming corrosive. Chemical treatment prevents corrosion and scale formation by adding corrosion inhibitors to the cooling water system. Nitrate-Borate based inhibitors are commonly used, while oil-based inhibitors are avoided due to reduced cooling efficiency.

Testing and Monitoring of Cooling Water:

Regular testing and monitoring of cooling water properties are essential for detecting any changes and ensuring system performance. CW samples are periodically drawn from the system and tested using test kits supplied by the inhibitor/chemical manufacturer. Parameters such as pH, total hardness, chloride, sulfate, silicate, and residue after evaporation are checked. Laboratory testing should be conducted once every three months, and the test results should be recorded for trend evaluation.


Maintaining proper cooling water systems, including the jacket cooling water system and piston cooling water system, is crucial for the efficient operation and longevity of marine engines. By employing chemical treatment, monitoring cooling water properties, and promptly addressing any issues, the risk of corrosion and scale formation can be minimized. This ensures optimal engine performance, enhancing the reliability and safety of marine vessels.

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