Blackstone labs came back with a TBN of only 5.1 after 2000 miles on this oil.... For those of us who have run 12,000-20,000+ mile drains with Amsoil for over two decades, this is clearly an indication that the test method is flawed. I recently ran a sample of this same Amsoil 5w-30 for 12,000 miles/1 year in my '95 Tacoma with about 0.5 qts of makeup oil and no oil filter change; using an Amsoil SDF-96, oversized filter. Results are posted in the UOA section from this analysis. The TBN came back @ 7.2, using the ASTM D-2896 method - this is roughly equivalent to a TBN of perhaps 5.5 using the more conservative ASTM D-4739 protocol that Oil Analyzers now uses.
In this 9000 mile sample, lead and copper wear are still well controlled and the viscosity is unchanged from the 8000 mile sample. If the oil were turning acidic, this is the first place to look for trouble. Since you added a quart of fresh oil after the 9000 mile sample, the TBN will be boosted a bit. The TBN of the 10k sample should be > 2.0; given the fresh oil and the wear metal concentrations will most likely go down a bit.
If this were my engine, I would have used a high efficiency, Amsoil Super Duty filter and changed it after six months, as per the Amsoil recommendations. But other than that, I see no reason to stop running the test. As for the 40wt nonsense, the baseline viscosity of this oil is approx 12 Cst, so it only has to thicken by about 5% to technically go out of grade. By comparison, Mobil 1 starts out at approx 10 Cst, so it would have to thicken by 25% to go out of grade. In other words, this is much ado about nothing....Most oil analysis labs will "flag" a sample when it thickens by 20% or thins by 10% and I believe those are reasonable parameters to use here. Amsoil could formulated a 30wt oil with a viscosity of only 9.3 Cst and it would technically never thicken out of grade. However, this reduced viscosity is NOT optimum in terms of minimizing wear and that's a more important consideration.
As a practical matter, I doubt you will find many LS-1 owners running drain intervals > 10,000 miles. If you are looking for the lowest wear rates for 6k-10k drains, there is no doubt that the Amsoil ASL product is performing the best of all the oils tested to date ....I don't expect any other oil, including Redline, to match the Amsoil wear rates after 10,000 miles of use.
Finally, since every engine is different, I strongly encourage folks to run their own comparison tests of Amsoil and any other synthetic. I think you'll find Amsoil provides the lowest wear rates over long drain intervals and holds up very well ....
Tooslick
www.lubedealer.com/Dixie_Synthetics