How To Collect An Oil Sample By Doug Salvesen Editor’s Note: We received the following letter from an avid and well-informed reader and felt his information was valuable in article format, so it is available here, as a Web Exclusive article. I read with interest the article on oil analysis (see “Oil Analysis,” PMM Dec.’ 07 ). As a lifelong boater, this subject is close to my heart. During a 32-year career in the oil industry, I have run all the physical tests in a company laboratory; I have driven trucks that carry lubricants; I have operated blending and packaging equipment to make and safely contain lubricants; and now I sell lubricants and interpret oil analysis for a living to some of the largest consumers of lubricants in industry. I found your information wonderful and spot-on. I would like to respectfully submit some additional thoughts to your readers, not about testing oils, but about collecting that all-important sample, the source of all this information. As the article pointed out, the elements and contaminants we are looking for are very small, therefore any level of distortion of the sample will influence the interpretation and potentially lead to an incorrect conclusion. So in addition to finding the right company to run the analysis, the responsible maintenance technician or owner needs to be very careful and purposeful about the method of collecting an oil sample. I have seen some statistics that as many as one in five samples are unusable due to sample contamination, and even higher waste if you consider labels that aren’t filled out effectively. The sample bottle should be kept with the top on, until the last practical moment before the sample is introduced to the bottle. A marine environment is rich with opportunities for contamination that is not part of the lubricant stream, especially engine rooms and bilges. Remember, we are endeavoring to measure very small, trace amounts of elements. In order to get a profile of the lubricant, the sample should be obtained before any top-off of lubricant and be truly representative of the system. There are basically three methods of obtaining a sample. I’ll list them in order of preference for obtaining a representative sample for interpretation. Capture the sample during normal operation, at normal operating temperature. This can be achieved safely via the installation of a sampling valve between the oil circulation pump and before the filter. There are several vendors that make durable sampling valves built for this purpose. These vendors also provide guidance on where to install these devices along the oil gallery to safely retrieve a representative sample. Vacuum extraction. This method can be used only on a system at rest (shut off). Get the system up to normal operating temperature for several minutes, preferably after a voyage of ...

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