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ENGINEERING BULLETIN | 98 - 6 |
| July 7, 1998 | ||
OIL ANALYSIS: USING THE RESULTS | |
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Effective oil analysis is the best method to accurately determine maximum oil and filtration service intervals. Oil analysis consists of various tests performed on each sample of oil returned to the laboratory. The results of these analyses, when compared, reveal lubricant condition, contamination levels, and wear rates of oil-lubricated components.
The results of an oil analysis provide information about several characteristics of the oil. An understanding of these results helps get the most life out of the oil. The characteristics of the oil that should be monitored, as recommended by most oil companies and other sources that offer oil analysis, are: viscosity, fuel dilution, water and/or coolant (ethylene glycol), total solids, and spectrographic analysis. Viscosity is the most important single property of lube oil. In used oil analysis, the test is performed to determine whether the oil has thickened or thinned excessively. Abnormal results indicate that some operational or maintenance defect exists that should be corrected. Fuel Dilution is the most common cause of oil thinning in diesel engines. Excessive fuel dilution is caused by improper operation, such as extended idling, low compression, and/or defects in the fuel delivery system. The results of fuel dilution are reported as percentage by weight or volume. |
Water can contaminate diesel engine crankcases as a product of combustion or due to coolant leaks. Water contamination is very seldom found in diesel engine oil samples. Engines that operate for long periods of time create enough heat to evaporate contaminating water. Most engine manufacturers set a maximum limit of 0.2% water contamination in their engines. However, evidence of ethylene glycol in crankcase oil indicates that coolant is leaking into the lube system and warrants corrective action.
Total Solids, the quantity of insoluble material in the oil, is a good general indicator of lubricant contamination level. Fuel soot normally accounts for most of the material measured in the solids test. Limits should be furnished by individual laboratories since test procedures and results vary considerably from one lab to another. Spectrographic Analysis assists in identifying abnormal internal wear, coolant leaks, and dirt contamination. Results are usually reported in parts per million. Accurate interpretation of test data is one of the most important parts of any oil analysis program. Continued use of test data and lab recommendations helps to provide users with an in-depth understanding of the test results. The user can combine lab results with maintenance history to derive a clear view of engine condition. |
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