# Black streaks in clean oil

Although there may be some, I'm not aware of any engines that retain 20%. But 15% is absolutely not uncommon.

From the factory service manual for my wife's Outback with the FB25 engine, total capacity at overhaul is 6.0 quarts. Filling amount when replacing oil and filter is 5.1 quarts. That calculates to 15% retained. For the Subaru 3.6 engine, total capacity is 8.2 quarts. Oil and filter change is 6.9 quarts for just under 16% retained. The numbers I quoted above for my old SL550 are from memory, and I may be off by a couple tenth's one way or the other, but you can see that it is about 17%.

With this knowledge, it helps understand why motor oil can look dirty almost immediately after an oil change. It is not that the engine is already making the oil dirty, but that the fresh oil has already been mixed with old oil.

Thank you but a point of contention is that we are not talking about the oil filter, we are squarely talking about the amount remaining IN THE ENGINE. We assume the oil filter has been removed for the sake of the dialogue, and MY estimate of 5-15%. If you take your numbers and subtract the 1/4 to 1/2 qt difference in the filter, I don't think any of your examples exceed 15%.

Thank you but a point of contention is that we are not talking about the oil filter, we are squarely talking about the amount remaining IN THE ENGINE. We assume the oil filter has been removed for the sake of the dialogue, and MY estimate of 5-15%. If you take your numbers and subtract the 1/4 to 1/2 qt difference in the filter, I don't think any of your examples exceed 15%.
We are absolutely talking about the amount remaining only IN THE ENGINE. If you will go back and read, all three examples I use are for the difference between total engine oil capacity minus the oil required to refill the engine after oil change, INCLUDING A NEW OIL FILTER.

I'm not sure what is so magical about this </= 15% threshold that you keep bringing up. Is it really that difficult to believe that some engines could hold 15%, and another 17%?

Really, this is all missing the point of this discussion. Whether it is 17%,, 10%, 5%, or anywhere between, even fully drained engines, with oil filter removed, retain some motor oil. So we will always see immediate "contamination" of the fresh motor oil with used motor oil. That should be understood and expected.