Quote:
Originally Posted by shertex
UNLESS the soot level, irrespective of the kind of oil that's used, typically hits a certain limit at 5000 miles. I think that's part of the logic of those who are uncomfortable with longer drain intervals: soot, even in suspension, is bad for the engine, thus we should always stick with the original recommended interval.
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That is essentially my thoughts. In old diesels, the oil will have a large amount of soot long before it chemically breaks down. I don't know how much is "unacceptable" but I doubt anyone could develop a single value. If we accept that any amount of suspended soot will cause some increase in wear, any "acceptable" limit would have to be based on an acceptable rate of wear for critical parts. Without any better data, I'll just stick to the manufacturer's recomemdation of 5000 miles.
I recognize that having a short interval due to soot loading somewhat negates the advantage of using synthetic oil, but I still think it's worthwhile for cold starting.