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Aluminum in engine oil

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Question: I just did my first oil analysis on my Cummins 6BTA diesel, and the results seem somewhat disconcerting. According to the report, there was aluminum in the oil at 28 ppm (parts per million) and iron at 20 ppm. The oil that was tested had approximately 43 engine hours on it. And since I bought my boat some nine years ago, I have religiously changed the oil in this particular engine every 50 hours or less. What can I do to either reduce the aluminum count or bring it down to zero?
—Richard S. Symms
Issaquah, WA

Professor Diesel: Regular oil analysis is one of the best preventive-maintenance tools. Analysis done on a regular basis establishes a history of normal engine wear and can be one of the first indicators of excessive wear and contamination.

Before panicking about your results, make sure that the oil analysis is valid. Your engine should be run until the oil is hot and mixed before you take a sample, and you should always take it from oil you’ve drained into the engine’s oil pan. Let a quart or so go first and sample what remains. (Hot oil can cause serious burns, so handle it carefully, and always wear protective hand, face, and eye gear.)

Unfortunately, taking an oil sample for the first time on a nine-year-old engine is likely to produce deceptive readings. The iron content you mention should not be a concern. The aluminum content, on the other hand, could be an indicator of piston or bearing wear. I suggest you take another sample, being careful to follow my directions. If the reading persists, contact your Cummins distributor for further advice.

A host of things can contribute to excessive piston and bearing wear. They include cold engine operation under load; over-propping or otherwise overloading your boat; full-throttle starts; failure to maintain the oil level to the full mark on the dipstick; using oil or additives that don’t meet your engine manufacturer’s specifications; and not following the engine manufacturer’s hourly maintenance schedules.

Professor Diesel is Larry Berlin, director of Mack Boring’s Training Services division.


This article originally appeared in the February 2011 issue of Power & Motoryacht magazine.