Ill just make a few points to add to this argument. I think it is kind of silly.
-Is M1 at 3000 miles better or the same as m1 at 0 miles? Well, let me ask this: If my car has a range of 500 miles, is a full tank of fuel any better for the car than a half tank? Its kind of the same argument. We know that oils have the necessary surfactants, etc to suspend and allow filtration of wear contaminants. So then where does this take us? Is an oil with TBN of 11 better than an oil with TBN of 6? Id say no. The argument is similar with any of the other additives. Considering the flowrate and movement patterns of oil in an engine, and also considering the residence time of oil in any one location, I think a TBN of 6 would still provide excellent protection in the respect of what the components that make up the TBN index number.
-Now, what about extended drains? Well, my father has driven his 94 toyota previa on dealer dino oil for 7500mile intervals, and the car has 165k and the engine is as strong as when new. No UOAs were done, just going by the book. Could you say that the dino oil in his engine at 3000 miles is worse than new dino oil? Sure. Can you say that it protected worse than the new oil? Perhaps, but, having an engine that is as good as new at 165k, with nothing ever being replaced, how can you argue with actual results? If youre implying that the engine would last twice as long by halving the oil change intervals, Id like to see that.
-Consider my engine: 5 cyl 3.0L MB OM617 engine. It has been documented that use of synthetic oils in this and the newer OM603 series engines reduces timing chain stretch by half. This was with 'extended' drains, based upon keeping the oil (Mobil1 15w-50 CF) to the point where soot was too high (around 1.9-2% by analysis, between 8000-10000 miles). What does this imply? That some mechanism for reducing wear or hard operating conditions exists when synthetic oil is used. (Info provided by Dr. Marshall Booth, MBCA technical advisor)
-Consider the two mentioned beginnings of UOA: railroads and Mack trucks. What are these engines? DIESELS!!! And what can easily become the #1 destroyer of diesel engines? SOOT!!! UOA is most commonly used to track when soot levels go past a preset amount (generally 2%), as then the dispercancy characteristics of the oil, the filteration and bypass system, etc. have been used to their fullest. I agree that it is not necessarily indicative of wear amounts, since the oil analysis is such a small quantity of the sump, but assuming a well mixed oil pan, can you tell me that the soot is not evenly dispersed? I know one thing, I dropped my oil pan after 215k miles, after a hot oil change, and there wasnt a sign of sludge in there. It was clean. No nothing, except the retainer ring for a green bottle top (?!?!!). No sludgy oil, no deposits, nothing. When I take the valve cover off for valve adjustments its the same thing. No varnish, no junk, everything is very clean, once I clean the black oil off of it. UOA can tell you if wear metals are high. Whether or not this is forshadowing something that will happen in 20k or 100 miles is unknown to me, but if I see things like elevates Si and higher than normal Fe numbers, I know pretty well that most likely an intake leak is present. Another example is my chevy s10. I am getting Na, K and glycol present. Does UOA tell me much about wear? no, Fe, Pb, etc were very low. But, I know that the contamination will cause problems down the road.
-On using metals to determine wear, I have a few things to say. My MB engine will show ~20ppm of iron at 3000miles (the same regardless if Delvac 1 5w-40 synth or delvac 1300s 15w-40 dino is used), and ~0.9% soot. This is common results for these engines. But, take one apart at 300k, and chances are you will still see the factory cross-hatching in the cylinders. Test the compression and oil pressure... all within spec. So does UOA show me anything? 22ppm of iron would be considered pretty poor in 3000mi on many of these UOAs. So in that regard, it doesnt tell much. However, the use of checking the trend of the wear, and having someone experienced explain it certainly can tell a lot. Quantitatively? maybe not... but in real life observations, if something goes awry and the engine is used for thousands more miles? Probably the useful life will be decreased. That is a question that Id liek to see answered. Especially since the MB engines can easily last 500k miles, so there is lots of data to be had.
I dont have much to say, but wanted to say something... So there you go
JMH
[ January 24, 2004, 05:14 PM: Message edited by: JHZR2 ]
