Lubricating Oil on Site Tests


The marine surveyor should pull out the dipstick and check that there is sufficient oil in the sump by reading the oil level against the marks on the dipstick. It should be noted that lubricating oil in a compression ignition engine is always black and, in a petrol engine, a dull yellowy-brown colour. He can then make some simple on board tests to check the quality of the lubricating oil in the sump. There are three of these tests: -


• the feel test, • the drop test, • the crackle test.


THE FEEL TEST:


For this test, he should rub the sample on the end of the dipstick between thumb and forefinger. The oil should feel smooth to the touch. If there is anything wrong with the lubricating oil this will be instantly discovered as the oil then will feel gritty.


THE DROP TEST:


If he feels this grittiness between his thumb and fore finger, the marine surveyor should then see if the oil requires further analysis by making a simple drop or dispersions test. The drop test provides quick and accurate visual confirmation that it is time to change a lubricant. Further, if the results of such a test are compared at regular intervals, oil change cycles can be determined for the particular engine, brand of oil and their use, all of which affect oil degradation. This is done by stretching a filter paper tightly over the top of a convenient tin or other receptacle and held in place by means of an elastic band and then dropping a blob of the oil onto the filter paper and leaving it to spread. Over a short period of time the oil slowly spreads out over the surface


42 | The Report • June 2017 • Issue 80


of the paper and drips through leaving any contamination behind as a series of coloured, concentric rings. A fresh sample of oil should be dropped onto the paper at the same time as the sample being tested for comparison purposes. The procedure is simple: -


• Withdraw the engine or gearbox dipstick and allow a generous drop to form on the end. Deposit the oil drop on the test sheet by lightly touching the end of the dipstick on the medium.


• Leave the test sheet in a horizontal position for a few minutes and then compare the sample to a sample of clean unused oil similarly treated.


• Backlighting samples enhances the sample results. This is done by simply holding the sheet up to a light or the sky.


THE CRACKLE TEST:


This test has been used as a reliable indicator of emulsified water, a go/no-go test. However, with practice and keen eyes and ears, the procedure can be advanced considerably and made more quantitative. Rather than simply listening for the crackle (which is due to scintillation), by adding visual observation of vapour bubbles, a rough indication of the amount of moisture present can be obtained. The revised method is referred to as the visual crackle. Success in using the procedure depends on practice with varying moisture concentrations in different common fluids. A laboratory syringe and a paint shaker can help create the experimental suspensions. While the visual crackle does not replace the need for other more precise techniques, it does provide vital information when and where it is needed. Simple, inexpensive on site tests such as this can make a real difference in the effectiveness of oil analysis and contamination control.


The hot plate crackle test is a simple test to identify the presence of free and emulsified water suspended in the oil, provided a few simple rules are followed.


1. Raise the hot plate temperature to 320°F (160°C). Always use the same temperature.


2. Violently agitate the oil sample to achieve an homogenous suspension of water in the oil.


3. Using a clean dropper, place a drop of agitated oil on the hot plate.


The marine surveyor should look for the following:


1. If no crackling or vapour bubbles are produced after a few seconds, no free or emulsified water is present.


2. If very small bubbles (0.5 mm diameter) are produced but disappear quickly, approximately 0.05 to 0.10 percent water is present.


3. If bubbles of about approximately 2 mm diameter are produced, gather to the centre of the oil spot, enlarge to about 4 mm, then disappear, approximately 0.1 to 0.2 percent water is present.


4. For moisture levels above 0.2 percent, bubbles may start out about 2 to 3 mm then grow to 4 mm with the process repeating once or twice. For even higher moisture levels, violent bubbling and audible crackling may result.


He should be wary of the presence of dissolved gases, fuel, refrigerants and volatile solvents, which can cause false positives.


H2 O


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