What type of lube oil system do both main propulsion and ships service diesel generators use?

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Large marine diesel engines use a closed-type lubrication system. This means the lubricating oil circulates in a sealed loop: a pump pushes oil through filters and coolers to the engine bearings, and the oil then returns to a dedicated reservoir where air is separated and the oil is kept clean before being recirculated. Keeping the system closed prevents oil from escaping or being contaminated by the sea air, helps maintain steady pressure and flow as the engine speeds up or slows down, and supports reliable filtration and heating/cooling.

This setup is ideal for both the main propulsion engine and ship’s service diesel generators because they demand continuous, high-quality lubrication to protect bearings and maintain performance under varying loads. In contrast, an open-type system would vent oil and air to the atmosphere, risking oil loss and contamination, which is less suitable for these critical, high-demand applications.