Major league baseball players who average two hits for every 10 at bats aren't likely to remain long in the major leagues. This batting average of .200 represents a level of hitting performance that is often referred to as the "Mendoza line," after either Minnie or Mario Mendoza. In engine oil analysis there's no equivalent of the Mendoza line. Put simply, there aren't any limits published by any engine manufacturer in regard to how much iron, or copper, or chrome, or other contaminant is too much. The important factor in using oil analysis is not the raw numbers indicating the quantity of metals in the sample—which are reported in parts per million (ppm)—but the amount of deviation from the engine baseline established by at least three previous samples. Oil sampling is one engine diagnostic tool and it's the most easily misunderstood. Let's visit the other diagnostic tools before we look at the art and science of oil analysis.
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