Originally Posted By: skyship
I would have thought you understood the difference between the oil grade and detergents. The oils used are shearing down rather too far for an extended OCI, so a different full synthetic would be better and it might be good to move up a grade if the engine is not OK for the equivalent of the mid 20's, because the final viscosity will probably be down to the teens by 10K if a 5/30 is used.
If the oil does not contain much Calcium it should have more Magnesium based detergents, but in a few cases of more expensive oils there might be other detergents in use, which is one reason why it would be good to see the TBN / TAN relationship.
More detergents and dispersants help to reduce the insolubles figure which is high for a short OCI, so again a better oil is needed for an extension beyond 5K miles, the other more sensible option might be a better long life oil filter.
There are only 2 reasons I can see for not extending to 10K miles and both might be resolved by changing to a major brand fully synthetic 5/40, BUT it would be better to use a long life oil filter, as I suspect the insolubles curve might reach the maximum.
The OP's engine is shearing the oil a lot for 4K, which is why I think a major brand full synthetic would be good, if it wasn't for the low viscosity figures a conventional would be fine.
So now your instead of actually answering my specific questions you insult my intelligence? Where in any of my posts do I ask what the difference between weight and detergents are? I simply asked HOW does being a 20 WEIGHT or 30 WEIGHT oil have a difference on a oil filter capacity. Once again just beating around the bush with any actual facts. How do you know that the oil wasnt actually cleaning something? It very well could have been extra wear but the UOA proves that wrong. If the oil has the same detergents, it should not make any difference in the filter capacity whether or not it was a 20w or 30w. This oil did shear some in a short OCI but for the current OCI how did this oil fail? What are you measuring your results against? For the OCI it had great wear results, isnt that what people are after the most? If the oil sheared but yet still provided adequate protection, is that a oil failure? Look at the synpower 5w30 UOA, it had higher calcium but yet higher insolubles for the OCI. According to your logic, that oil performed worse even though it was a full synthetic?