because other problems such as high top end wear associated with blow by will manifest themselves first. Nitration in industrial oil samples is an indication of a thermal breakdown of the oil. This can occur when the oil comes into contact with extremely hot surfaces or where excessive aeration, particularly in hydraulic systems, leads to microdieselling. Though not often seen, an increase in nitration should be taken seriously.


Gas chromatography (GC) is a separation technique used to analyse used engine oils for evidence of fuel dilution. The technique as applied to fuel dilution measurements is used to separate and measure two volatile fractions of specified boiling ranges from used engine oil samples. The first volatile fraction of interest has a boiling range similar to that specified for gasoline, while the second fraction has a boiling range similar to diesel oil. The instrument is calibrated and measurements are reported as a percentage contamination by mass. The fuel dilution test is typically performed either when a significant drop in sample viscosity is measured, or when the flash point test has failed.


It is important that the


oil brand and grade are correctly described to the laboratory if problematic samples are to be detected. Special care is necessary in interpreting results because many factors can influence their interpretation. Fuels are complex mixtures of organic compounds that are classified into products based largely on distillation ranges rather than specific chemical data. There are also significant overlaps between various product specifications, making it sometimes difficult to accurately separate and quantify fuel mixtures.


It is frequently found that high sodium and copper in the analysis may indicate a


leaking oil cooler. A leak in the oil cooler puts water into the sump oil which very quickly forms a foamy green sludge which can be seen on the dipstick or inside the rocker cover.


Intercoolers, if fitted, are


a different issue. When there is an internal leak in an intercooler then there will be salt water in the cooling system, not in the oil system. Engine oil pressure is many times higher than either sea water or engine coolant pressure.


If the


intercooler is bad, then sea water would be injected into the cylinders which would result in a locked up engine.


would be a visible oil loss then a milk shake after cooling off.


If the oil cooler is bad, there If the


manifolds or risers are leaking there would be a loss of compression and an eventual engine lock up resulting in bent connecting rods. What sea going engineers call a hydraulicking. When a small amount of salt water enters the hot oil, the water evaporates and the salt remains in the oil. That results in no emulsified water and probably no further damage.


If high sodium


and copper values are found, therefore, the marine surveyor should consider recommending the opening up of the coolers and have them inspected/tested but he will find that many people disregard such preventative maintenance. He should also know that it takes very, very little water to cloud the oil and, therefore, even minor leaks are usually apparent.


It is also true that


sodium values do not necessarily mean the presence of salt water. Depending upon the engine, pulling a valve cover may be a hands on method of seeing if there is an issue with residual water in the engine. One old school approach is to push the marine surveyor’s index finger in the cover and to feel the underside of the upper surface for thick sludge which is a clear tell-tale for water in the engine.


NOX


A little salt in the oil after a cheap repair is to be expected. The marine surveyor should


check to see if the engine’s air intake is baffled to separate the rain or sea spray from the intake air. After a riser failure, the engine should be filled and flushed with diesel fuel while turning it over by hand to remove residual contaminants.


The most common sources of sodium are seawater, coolant and dirt the first two being most likely in a marine application. Other elements present in the oil analysis will give clues as to the source of the water.


If the analysis shows


silicon and phosphorus then the probability is that the defect lies in the coolant and, if not, it is most likely seawater.


The marine surveyor should know that simply determining whether coolant or sea water was the cause of saltation based on one oil sample may be misleading. The ppm of the metal components will indicate if premature wear and tear exists. Assuming regular oil changes, an engine should have very low ppm for the metal components. For a coolant leak there should also be high levels of boron due to the presence of antifreeze. A mixture of antifreeze and oil will cause premature wear and tear.


If salt is found, then the cooling and oil systems should be drained and flushed out with distilled water. The cooling system should then be filled water and a new oil filter added to the engine. The engine should then be run until it is hot enough to remove all the crud i.e. for about 45 minutes. Then another oil and filter and coolant with the correct mixture of antifreeze change should then be carried out. That should leave reasonably clean systems as a starting point. After a further ten hours of running another oil sample should be taken and analysed. If the engine is showing signs of wear and tear then increasing the frequency of the oil and filter change with a good grade oil will help to keep it going. Maintaining coolant condition avoids corrosion and elevates the boiling point level.


The Report • June 2017 • Issue 80 | 41


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