Saltwater contamination of the lubricating oil may also cause bearing burnout. Water, in small amounts, is always present within the lubrication system as a result of condensation. Air which enters the units contains moisture. This moisture condenses into water when it strikes a cooler surface and subsequently mixes with the oil. The water displaces the oil from the metal surfaces and causes rusting.
Water mixed with oil also reduces the lubricating value of the oil itself.
When the main engines are secured, the oil should be circulated until the temperature of the oil and that of the reduction gear casing approximate the engineroom temperature. While the oil is being circulated, the cooler should be operated and the gear should be jacked continuously. The purifier should also be operated to renovate the oil while the oil is being circulated and after the oil circulation is stopped until water is no longer discharged from the purifier. This procedure eliminates condensation from the interior of the main reduction gear casing and reduces rusting in the upper gear case and gears. Generally, lubricating oil will be maintained in good condition if proper use is made of the purifier and settling tanks.