Engine Oil and Lube Oil Quality

Engine Oil and Lube Oil Quality
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Importance of Oil Quality

We have been studying about Marine diesel engines and know that lubricating oil system is an important part of the engine system. The properties of lubricating oil need to be maintained within the specified parameters, in order to the engine to operate smoothly and efficiently. In this article we will take a look at the hazards of low quality engine system oil. I am sure you know what is viscosity and what is its relevance to engine running.

Regarding the quantity of engine oil, the empirical rule states that the amount of system oil depends on the type of engine.It should be 1lit/bhp and lube oil should not circulate more the 15 times/hr.

  1. If very low quality of system lube oil is maintained in circulation ,function of lubrication will be disturbed.
  2. Less amount of lube oil in circulation causes rise in temperature thus reducing the viscosity leading the failure of boundary lubrication due to decrease in oil film thickness.
  3. Insufficient time for de-aeration and it accelerates the process of oxidation of oil .Due to oxidation
  • Lubrication oil properties are lost
  • Forms sludge and high temperature sludge adhere to metal surface.
  • Formation of acids/corrosive attack.
  • Increase the viscosity of oil.

4. Increase in friction ,wear,heat corrosion,contamination and noise and it reduces the engine performance to critical and in extreme cases total shut down of engine operation.

5. Also other properties of lubricating oil will be lost sooner as the additives will deteriorate faster.

Lube Oil

Problems Associated with Lub Oil Viscosity Change


  1. Unable to form a lubrication film and losing the lubricating property.
  2. Increase in friction and wear and bearing damage.
  3. Over heating due to break down of lube oil film.
  4. Acid corrosion occurs if contaminated by high sulphur content HFO.
  5. contamination with diesel oil reduces the flash point.


  1. Fuel contamination - viscosity increases due to HFO and the viscosity decreases due to DIESEL OIL contamination.
  2. Contamination of insoluble like carbon from blow past.
  3. oxidation-Increase viscosity.
  4. contamination by other lubrication-Due to accidental topping up of wrong grade of lube oil.
  5. Less quantity of lube oil in circulation.


  1. Preheating of lubricating oil before purification for effective functioning of purifier.
  2. Purifier efficiency reduces contamination of insoluble and water regularly clean the sludges formed in purifier.
  3. sufficient quantity of lube oil in circulation.
  4. proper cooling of lube oil before sending to the engine.
  5. After circulation for the certain running period " BATCH PURIFICATION " is done .
  6. carry out shipboard lube oil test.

what do you mean by “BATCH PURIFICATION”****:

  • Originally the term batch purification applied only to the purification of MAIN ENGINE crank case lube oil.
  • Batch purification referred to the system whereby the engine is shut down and the whole of sump lube oil charge is pumped up to the dirty lube oil tank in the upper part of the engine room.
  • The lube oil is heated in the tank and left as long as possible to settle out solids ,sludges and any water .
  • It is then slowly purified in one batch ,hence the name.
  • It is generally done in port where main engine is not running.while running of main engine we cannot do the batch purification because the regular continuous purification will be going on .

Treatment of Lube Oil

Concentration of acid, water and in adventitious solid matter is prevented by continuous filtration of lube oil circulating in the system. Ideally the entire flow of oil should be filtered before admitting into the engine bearings. But in practice this presents some difficulty. In order to achieve finer filtration filters of fine meshing should be introduced in the flow path. The arrangement run the risk of starving the bearings as the flow resistance is increased. The other solution is to do finer filtration through bypass arrangement. The best method would be to operate with two oil chargers. While one charger is circulating in engine the other charger is purified in settling tank and then through centrifugal separators. Moderately fine filters are installed in the flow path of primary circuit which would reduce load on filters and also increase the time interval between cleaning.

Ship Board Oil Test

Qualitative oil test carried out in board ship do not give a complete and accurate picture of the condition of lube oil .This could be obtained in a laboratory.

However they do give good enough indication of the oil to enable the engineer to decide when the oil should be replaced or if some alteration in the cleaning procedure is considered necessary.

Test for Alkalinity,Dispersiveness,contamination ,water and viscosity are usual.

samples of oil should be taken from the main supply line just before entry into engine since it is the condition of the oil being supplied to the engine that is of the greatest important.

Image Credits:

Wikimedia Images - Lube Oil