I did a search of Mobil, Pennzoil, Valvoline, Havoline, and Quaker state. I picked these oils because that is what I believe is in the majority of cars on the American road. Unfortunately, the boutique and custom blended oils are unknown by most.
Of the above oils, only one 10W-30, that was not a high mileage oil, had a 100C cSt of 11.0. All the other 10W-30's were lower than 11, some only a 10, at 100C. The 5W-30 oils ran up into the 11.0-11.4 100C cSt range.
According to the Frequently Asked Questions, Ask An Expert, Technical Information, or whatever of the different brands web sites, the difference in Viscosity Index Improvers between a 5W-30 and a 10W-30 was very small and the 100C cSt of the 5W more than made up the difference..(the reason the 5W's have the higher 100C cSt?) I thought it took viscosity index improvers to make the difference but a manipulation of the base oils can make a difference. That is their talk, not mine.
The HTHS of non high mileage 5 and 10W oils was virtually identical. There were some 5W's that had a better HTHS and some 10W's that had the better HTHS.(I think HTHS is extremely important)
The viscosity index is a measure of how much the oil's viscosity changes as temperature changes. A higher viscosity index indicates the viscosity changes less with temperature than a lower viscosity index. The 5W-30's oils had the better average Viscosity Index over the 10W-30's, but, I think that is a property of the thicker base oil,(someone help me here)
I went back 100 pages(I was going to mow today but it has poured the rain)) on the UOA. I looked only at 5W and 10W in 30 grade oils, synthetic only, no high mileage oils. As you might think, extremely varied, but this is what I averaged out: (please note that this work is more lavatory than laboratory)
5W-30=average OCI=6311....average 100C cSt=9.63....average starting cSt=11.2....14.91% shear..HTHS 3.04
10W-30=average OCI=6133....average 100C cSt=9.57....average starting cSt=10.3....7.09% shear....HTHS 3.16
What this tells me is that most 10W oils will shear less, much less, than a 5W oil.
The oil companies, naturally, know this so they start the 5W's out with a higher 100C viscosity.
I said in an earlier post that I believed it would take a 5W-30 with a cSt of 11.3 more miles to shear sown than it would take a 10W-30 with a lower cSt to shear down. I was correct, but just barely. I had no idea that a modern synthetic 5W oil would actually shear this much and would have argued with anyone that said it would.(that is only the second time that I have been wrong. The first time is when I though I had made a miste.....mista....mistoo....error)
After about 6000 miles, the 5W and 10W are near equal with the 5W actually having a slight edge even though they shear considerably more. What I don't know is what is the by-product, if any, of shear down.
Without knowing and understanding the addative package, the above information is basically meaningless but kept me entertained for a while.
What we can't see on oil Company spec sheets, or at least most of them, is stuff like moly, boron, calcium, ZDDP. Some do not show Noack or TBN. We can ususally find ZDDP if we look hard enough of we can look for an ILSAC rateing.
I don't know if Gary or Pablo can tell us anything about Moly, Boron, and Calcium in the Amsoil top 5W-30 and 10W-30, but the rest of the specs are very impressive. The ATM spec, as to what it does show, looks like the best "STANDARD" 30 grade oil out there, giving the High Mileage oils a run.
If you look at the spec sheets, the 10W-30 high mileage oils stand out as compared to the "STANDARD" 10W-30 oils. They usually have excellent 40C and 100C cSt, VI, and HTHS. But most don't show TBN or Noack.
If I were going to use an over the counter 10W-30 oil, it would be Mobil 1 10W-30 High Mileage. If I were going to use a botique 10W-30 oil, it would be amsoil ATM. This based on what can be obtained from spec sheets and UOA.
Cofee
The full synthetic Maxlife is one of the high mileage/heavy duty type oils. It starts out higher than a 5W-30 and shears less.
