The Noack test is run @ 482F so that you can accumulate data in a reasonable amount of time. It's an accelerated aging type of test of the kind that 's used all the time on polymeric materials.
The Amsoil "thickening out of grade" situation occurs for several reasons:
Their 5w-30/10w-30 oils were formulated at the very top of the SAE 30wt range, so they were borderline 30wt/40wt oils to being with. As little as 5% thickening would technically cause them to thicken out of grade. Combine this will extended service intervals and you'll see them thickening by up to 20%-25% in some cases. The worse condition for this is short trip driving in a cold climate, where fuel and moisture drive the rate of oxidation. GM Vortec engines in particular also generate lots of copper from the cam bearings and this is a catalyst for the oxidtion reaction. Some bench tests (RBOT, TFOUT) actually use copper strips to accelerate the oxidation of lubricants under controllled conditions.....
The S2000, 0w-30 situation is a bit different as it's been formulated closer to 11.0 Cst since it hit the market. In this case I do think some of the thickening is due to burning off of the low molecular weight components blended in to get the 0w rating @ -35C. In addition the average service interval for this oil is much longer than for any other oil tested on the BITOG site. When you try to run very long service intervals - particularly in V-8 engines with small sumps - you get a great deal of fuel contamination. This drives up the total solids level and results in oxidative thickening if you run service intervals >> 10,000 miles.
My recommendation for these V-8 applications is to use one of Amsoils', "diesel formulated" CI-4/SL chemistries. The Series 3000 5w-30, the new 10w-30/ACD or the 5w-40 are all going to do a better job or resisting this fuel related thickening then the TSO/ASL/ATM formulations. The reason is that the diesel oils are designed to suspend and disperse large amounts of soot and this attribute will also help them deal with the fuel related contamination you get in a gas guzzling V-8 that only has a 5-7 quart sump....
I should note that the recently reformulated Amsoil 0w-30/5w-30/10w-30 are now midrange 30wts, with viscosities @ 100C in the 10.5-10.65 range. So I don't think you'll see them thickening out of grade the way they used to do. Of course the Amsoil bashers will have nothing to complain about then...
LOL!
Tooslick
Dixie Synthetics