Per OP's original post...
Mileage intervals: 5k, 11.2k, 15.8k, 21k, 26k
Fe 5, 13, 21, 42, 62
Cu 3, 10, 16, 39, 66
Mileage between reported samples: 5k, 6.2k, 4.6k, 5.2k, 5k.
The important thing to look at here is the change in wear metals between intervals, not as an accumulated average.
Using the following formula [(Accumulated miles - Previous sample miles)/(Accumulated wear - Previous sample wear)],
wear rate per thousand miles between reported intervals (either as XXFe/1k mi or XX Cu/1k mi):
Fe: 1, 1.3, 1.7, 4.0, 4.0
Cu: 0.6, 1.1, 1.3, 4.4, 5.4
I'm in complete agreement with your numbers.
What I'm curious about is the Si in the last two UOAs, so let's add Si to your numbers:
Per OP's original post...
Mileage intervals: 5k, 11.2k, 15.8k, 21k, 26k
Fe 5, 13, 21, 42, 62
Cu 3, 10, 16, 39, 66
Si 5, 11, 15, 25, 33
Mileage between reported samples: 5k, 6.2k, 4.6k, 5.2k, 5k.
The important thing to look at here is the change in wear metals between intervals, not as an accumulated average.
Using the following formula [(Accumulated miles - Previous sample miles)/(Accumulated wear - Previous sample wear)],
wear rate per thousand miles between reported intervals (either as XXFe/1k mi or XX Cu/1k mi):
Fe: 1.0, 1.3, 1.7, 4.0, 4.0
Cu: 0.6, 1.1, 1.3, 4.4, 5.4
Si: 1.0, 0.0, 0.8, 1.8, 1.6
I corrected the starting value of the added Si in the first 5,000 mile UOA, as the Si in this virgin oil is know.
We did see the increase in wear metals at the 21,000 mile UOA and discussed dumping the oil and starting fresh. However, we were curious about how long the TBN would hold out, if the increased wear was caused by the carbon loaded oil filter, and if the increase in Si from the loaded air filter. The TBN held out really well and probably could hold out for another 5,000 miles. The new oil filter run from 21,000-26,000 miles was also loaded with carbon being cleaned from the internals, since we didn't see a decrease in carbon, we can't tell if the carbon is what is causing the wear. More Si was added to the oil between 21,000-26,000 miles. The air filter was changed at the 21,000 mile sample, but Si continued to increase in the oil. It could be that Si increased because of the filter being change and the airbox being disturbed and/or more Si made its way through the intake system and into the engine. I'm going to recheck the intake system for leaks.
What did we learn?
- This oil has very good TBN retention, which is important for an extended drain oil.
- This oil has very good oxidative stability, which is important for an extended drain oil.
- This oil has a high ability to clean, which also means it has the ability to keep an engine clean.
- My engine has carbon deposits that continue to be cleaned from the internals.
- My engine has a problem with silicon ingestion.
- The extra wear metals are probably caused by the Si ingestion.
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