7 Detrimental Effects of High Water in Engine Lubricating Oils.



Water – an elixir for all living beings on Earth, but not for an engine lubrication system. The amount of water in lubrication oil is one of the most important parameter which decides the life of running  engine parts. Water can enter the engine lube oil system through many ways including but not limited to:

  1. Engine Coolant leak,
  2. Moisture ingress/condensation,
  3. Oil cooler leak and thus water ingress,
  4. Steam heating line leak and
  5. Fresh oil contaminated with water.

The destructive effect of water on bearings can be more detrimental than that of particle contamination. Even a very Small quantity of water, say >500 ppm, can substantially reduce the service life of white metal as well as roller/ball bearings.

  1. Water in lube oil can damage directly on the surface or through a chain reaction. For example, water may lead to oxidation of base oil and the oxides combine with more water and generate corrosive acidic substances.
  2. Water can lead to hydrogen induced fractures where hydrogen is generated through the corrosion process aided by water or through the separation of hydrogen and water atoms at very high pressures. Pitting, etching and fretting are also speeded up in the presence of water in bush bearings and other bearings.
  3. High temperatures flanked by metal particles and water will eat up the antioxidants rapidly and deny the oxidative properties of the lubricant. All the other additives in the oil also suffer depletion in the presence of water. Water also forms sludge and emulsions which can block the oil passages starving the bearing surface of lubricants. Air can weaken oil films, increase heat, induce oxidation, cause cavitation and interfere with oil flow.
  4. Water’s viscosity is only 1 cSt and naturally if water is present in between rubbing surface, the surfaces can make contact and get damaged.
  5. Water is a promoter of micro-organisms such as fungi and bacteria and microbial contamination is also corrosive.
  6. Long idling in wintertime causes water condensation in crankcase, which leads to loss of base number and corrosive attack on surfaces, oxidation of the oil, etc.
  7. Emulsified water can mop up dead additives, soot, oxidation products and sludge. When mobilized by flowing oil, these globular pools of sludge can knock out filters and restrict oil flow to bearings, pistons and the valve deck.

Given all these harmful effects of presence of water one should first test for water content and should also have a plan for reducing the water content. One of the most economical and effective ways is to fit desiccant breathers on tanks. These will not only prevent moisture from entering but will also absorb moisture that is trying to evaporate from the oil sump. In addition they will also capture all the oil particles. Centrifugal separation is one of the best ways to separate water from engine oils.

How Much Water is allowed in Engine oils:

The answer to the above question is best stated by respective engine makers. However as a general rule of thumb, whether it is a 2 stroke cross head engine or a 4 stroke trunk piston engine – the maximum allowed water % in the main lubrication system is 0.3%. Man B&W states that the engine can tolerate water up to 0.5% for a short time. Thus it is always suggested to stick to a maximum water % , which can be allowed for safe engine operation is upto 0.3%.


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