question about metal waer.

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May 23, 2004
If 3000 miles UOA shows 2 ppm Iron and a 6000 UOA shows a 4 ppm Iron, then we can conclude that wear has not increased! Am I correct? I noticed that some of low mileage UOA show very small wear metal and people get excited about but when a 20K UOA shows 20 PPM metal wear we tend to look at it negatively!
I am sure some of the more knowledgeable members around here will sort out any mistakes I make in the following explanation. The following is as I understand it. That is the theory. However in practice you will find wear metals often spike when oil is first changed. You might see 3 ppm after 1000 mi, 5 ppm after 2000 mi, and 6 ppm after 3000 mi. This is why it is usually recommended a oil go at least 2500-3000 mi in order to get a representative UOA. When going to extended OCI with UOA you are looking for two things in order to set OCI. 1. Absolute limits: Minimum TBN and Maximum Wear Metals: 2. Any Evidence of sudden rapid TBN loss or sudden spiking of wear metals. 3000 mi - 6 ppm 6000 mi - 8 ppm 9000 mi - 10 ppm 12000 mi - 13 ppm 15000 mi - 18 ppm 18000 mi - 30 ppm 21000 mi - 50 ppm In the above example the 12000 mi UOA was not enough to be considered spiking but by the 15000 mi UOA it was obvious the wear metals were begaining to spike and the oil should be changed. 0 mi - 12.0 TBN 3000 mi - 9.0 TBN 6000 mi - 8.0 TBN 9000 mi - 7.0 TBN 12000 mi - 6.5 TBN 15000 mi - 4.5 TBN 18000 mi - 2.0 TBN 21000 mi - 0.2 TBN In the above example the sudden drop in TBN at 15000 mi would tell you it is time to change the oil even if you had set your absolute limit at 2.0 TBN. Gene
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