SpitfireS

Ok.. I see now this paper is "just" about Noria explaining how they defined their limits and I assume they would recommend their costumers to change the OCI if their samples would reach / exceed their limits.

Would the quality of the used fluids change the limits though?
6 years is a long time in oil R&D.
I mean, what do you recommend if a better fluid holds up longer?
Do you extend the OCI or do you lower the limit - and keep the OCI?

INDYMAC

I agree with both of your comments. I've also noticed that all TBN's are not created equally wrt effectiveness, resulting in a false sense of security. Some engine oils start and end with high TBN (reserve alkalinity) values, yet allow TAN to rise rapidly at some point. Yet some engine oil formulas start with a relatively low (6-8) TBN and end low, but hold TAN well in check throughout the entire OCI.

For Honda MTF II (MTL) I've noticed that rapid shearing causes poor subjective performance, not oxidation or sludging causing wear issues. I have Amsoil MTF in it right now and will test it when it's toast.

Gear oil in the diff is a little easier to evaluate, even without a UOA. The magnetic drain plug and a visual inspection of the used oil can tell a lot about oxidation and sludging as well as metal chunks and slivers on the plug. But I have seen a couple of UOA's with unacceptable wear rates on short OCI's. I've been told that temps above 180F is where sludging starts on gear oils.