Like many of you on this board, I have been sitting back and looking at oil analysis, filter info, and engine designs. Something has really struck me as interesting and I'm not sure I am ready to share this, as there is a little more that wanted to do before bringing this up but I suppose now is as good as any.
What I'm seeing is that many lower viscosity oils are providing more protection than that of thicker oils. OK, lets look at what I see.
To provide the best protection in a bearing, you want to created the best hydrodynamic cushion between the bearing and crank. This is done how? Oil pressure or oil flow?, Thicker oil takes longer to move through the system, therefore it takes longer to move through the shear zone(bearing/crank in this case). Thinner oil, well, it means it can maintain pressure constantly on acceleration and start up than a thicker oil. Ok, bear with me, lets move back to the oil filter.... Here is something I have recently found.. I took a synthblend, with m1's filter, and found it to work well, or did it? I then took a fram filter, with a mineral oil with the same additive package as the blend, and same viscosity as the blend, and it returned with lower wear numbers. Hmmmm, Ok, so only real difference here is POA on blend, ver's a mineral without PAO, and m1 high filtration, ver's a low end higher flow fram filter. Now, the mineral had better flow through the fram filter than the blend did in the m1 filter. This created more constant pressure at the bearings.
OK, at idle, say the engine is at 28lbs of pressure at the filter in and out to the bearings. Pressure gauge is sitting between the bearing and the output side of the filter. Now, when you accelerate you engine, the pump puts out an immediate amount of flow, so it will jump from 28lbs of pressure between the oil pump and the filter to 40-70lbs. This is not reflected on most pressure gauges that fast because two things.. One, the filter cannot pass that much pressure through at once, therefore it takes a moment for the pressure difference to open the bypass valve which during this time, you've sheared the oil out between the bearings and crank. Second is most gauges do not reflect immediately like a fuel gauge, it takes the gauge a moment to rise. There is actual fast reacting gauges but for cost benefits in cars, they opt for the cheaper one.
Now, back to flow, pump jumps up immediately, oil filter has high pressure momentarily between it and the oil pump and at the same time, bearing is squeezing the 28lbs of pressure you had in the bearings, while the filter at the same time is now trying to equal out the different pressure between the input and output sides., This, creates minor scuffing. With a thick oil in the bearing it will take longer for it to shear out, but at the same time, it will also take longer to get through the filter during this acceleration. On the other hand, if you can maintain higher flow to the bearings with a lower viscosity, it can slow down the shearing due to the fact you now have more pressure increased to the bearings faster than with a high viscosity oil trying to get past a high filtration media and having to go through by pass every time acceleration incurs. This is why you have a severe condition while driving in town vers on the hwy. The in town driving sees more stop and go, and more wear can occur because of these pressure/flow ups and downs where as on the hwy, flow is more constant and provides a steady pressure at the crank bearings where it doesn't tend to shear as much.
Another thing to think about, when racers line up to start a race, what are they doing?, they are running up the engines and are holding oil pressure up so when they jump on it, the pressure is already at the bearings and not at idle. Yes, there is more to it than that but that IMO, is one reason for having the rpms up as well as taching up for power.
So, point I'm making here is this... There is a balance of viscosity oil used vers, oil filter flow for each type of engine and for driving conditions such as temps, types of acceleration and drivers of each vehicle. You'll notice that the little old lady that never jumps on the gas seems to never wear a car out, unlike the younger guy who seems to rag em out quickly. One never breaks hydrodynamic lube as she accelerates slowly giving that oil a chance to build up pressure before scuffing and the other is on it quickly having sheared the oil out before the oil pressure gets there to assist maintaining hydrodynamic flow.
So, if you can maintain pressure at the bearings, this would reduce oil shearing, which would reduce bearing scuffing and higher heat due to the scuffing.
This is just some observations and my thoughts as to why some of the thinner oils may be producing better numbers than some of the thicker oils. Go ahead and tear it apart and let me see where the flaw is on this.