First off, don't be put off by the title....I don't mean to exclude those who CAN'T speak with authority (for then I would have to exclude myself).

Everyone agrees that AGGLOMERATED (BTW, a great vocabulary word to toss out in casual conversation... "You kids need to stay together and agglomerate so I can keep an eye on you.") soot is bad/evil and must be avoided. This, as far as I can tell, is a function of the quality of the oil. Delvac 1, for example, can handle at least 4% before agglomeration (clumping) occurs.

However, apparently even NON-AGGLOMERATED soot can cause damage (this on the authority of one of the guys in the lab that did my oil analysis).

The question is: what level, for all practical purposes, is perfectly safe?

At least Marshall Booth (well nigh the patron saint of all things Mercedes diesel) used the figure of 2%....and I think Mercedes published that figure at one point, but now I'm not sure. So my operating assumption has been that, as long as I'm well under 2%, I am, oil wise, doing what I can to maximize my engine's longevity.

But, there appears to be a school of thought that ANY amount of soot is harmful and that, therefore, it should not be allowed to rise above x%. I've seen 1% as the safe threshold. But where does that come from? And how is it not arbitrary? Why not 0.5% or 1.2%? If ANY amount is harmful, then why shouldn't we change our oil every 1500 miles or whatever? I like to save money as much as the next guy, but I'm really willing to spend whatever I have to on oil and filters to ensure extremely long engine life.

Honestly: If thought that changing my oil every 1,000 miles would promote engine longevity, I would do it. But I have no reason to believe that.

Currently, my plan has been 10,000 mile drain intervals, which would equate to about 1.4% soot. If that sounds like a risky plan, could someone please explain to me why it is risky?

Thanks in advance for contributing to the discussion and helping me to grow in my understanding of these things.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 179k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 77k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife