Onboard Lubricating Oil Tests

(By Kamal Hossain, Chief Engineer)

(a) Explain how lubricating oil can be tested onboard.


L.O can be tested on board by using Maker’s supplied test kit , which can give the result whether it is safe for further use or not.
For L.O test , sample oil must drawn out from correct point , such as from test cock or from pump’s discharge pressure gauge connection. It should not be drawn out from , filter out let and purifier out let .
Sample oil must be taken with standard plastic tube with seal for both on board test and Lab. analysis.

Acidity Test

– Release a drop of sample oil onto the blotter paper. Then wait about 5 min. allow to spread itself.
– Add a drop of indicator solution ( Potassium Hydroxide ) onto the spread area of sample oil. Then wait about 5 min
– Acidity can be determined by color change of sample oil.
– Bluish Green means: – No acidity in sample oil , it is alkaline stage.
– Yellowish Orange means: – Neutral stage , but no longer satisfactory.
– Reddish Color means: – Acidity in sample oil , not fit for further use.

Another test is extracting the acid from sample oil , known as Ph. Test.
– Mix unknown amount of distilled water to sample oil and shake well.
– Then mix with known strength of indicator solution
– Compare with a series of color standard each representing their Ph value .
– Determine Ph value of sample oil quite accuracy.

Fuel Oil Contamination Test ( Viscosity Test )

Fuel oil contamination with L.O may cause by dribbling fuel valve and leaking fuel pump due to excess wear of its components. When L.O is contaminated with fuel
– L.O color change to dark brown
– Flash point become low
– Viscosity decrease

If fuel oil contamination is occurred , viscosity of L.O to be tested for determination , whether fit or unfit for further use.
– The viscosity test can be done 3 tube rolling ball viscometer
– One tube is filled with used sample oil . ( Let say its viscosity grade is SAE 40 when fresh )
– Fill lower and higher viscosity fresh oil into another two tube each and individually ( Let say SAE 30 & SAE 50 oil )
– Then placed all 3 tube in hot water contained plastic bucket to allow same temperature for a moment.
– Mount all 3 tube in tilted board and inverted. Internal hollow ball in each tube will rise to surface.
– If the time taken by ball in sample oil tube is between the time taken by remaining two ball in their tubes , it means that , the viscosity of sample oil is fit for further use.
– If not , contaminated L.O must be changed.

Water Dilution test

Water may dilute in L.O from…
– Condensation from vapour in the crankcase
– Leakage from Cylinder cooling system ( i.e , JK seal from liner )
– Leakage from steam heating of sump tank.
– Sea water cooler tube..

Water dilution can be check with a Crackling test.
Take sample oil with test tube and heated up while shaking .
If there is no crackling sound , oil is dry.
If there is a slight crackling sound, the oil having trace of water.
If there is heavier crackling and frothing , the oil is heavily diluted with water.

Insoluble Content test

It is very simple test use with blotter paper.
Release each single drop of sample oil and similar fresh oil with known insoluble content . Wait for complete spread of both oil drops.
Compare the two oil spread condition and determine the content result of test oil.
For straight mineral oil , test result should below 1 ~ 1.5 % of upper limit.
For detergent/dispersant oil below 5 % of upper limit.

(b) How will you rectify in the case of lubricating oil which has been contaminated with a certain amount of sea water.


Lubricating Oil can be contaminated with sea water due to leakage from air cooler tubes and L.O cooler tubes. It is mostly happen while engine is stopped. Contamination of sea water can be detected by abnormal rise of sump oil level abnormal water discharge from L.O purifier and colour change of L.O .
If certain amount of S.W contamination with L.O is detected , batch purification method is recommended . For the successful purification , the following process should be done.
– Transfer the whole quantity of dirty L.O from sump tank to a storage/renovating tank .
– In this tank , L.O to be heated up to 60 ‘C by provided heating arrangement and allow to settle at least 24 hour. While settling , water and sludge from L.O to be drained out frequently.
– At this time , open up M.E crankcase , both wet and dry sump tanks , properly ventilated , thoroughly wipe out and cleaned , make inspection and closed back . All L.O piping to be drained out.
– If condition of L.O in renovating tank is found satisfactorily free from water and sludge in drainage , start to purify with L.O separator , renovating tank to renovating tank circulation process.
– To achieve optimum purification effects
– Use correct size of gravity disc
– Minimum feed rate
– Heated up inlet oil to 77 ~ 82 ‘C by purifier heater
– Water washing by using warm water.
– Frequently de-sludge the purifier
– During the process , possible sources for Sea water ingression to be rectified and pressure test to be done , to
make sure no further sea water contamination.
– L.O acidity , viscosity and water content test to be done frequently and keep batch purification process until test results are satisfactory.
– Then release L.O from renovating tank to sump tank via purifier outlet for normal engine operation.
– Even though the test results are found satisfactory , Oil sample to be sent for laboratory analysis for further recommendations.

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