overkill, wishy wash it all you want, maybe you need to study it a bit more.
I'm a glutton for punishment I guess, but let's go over this again.
You stated:
Exhaustgases said:
the base oil is the low number, the viscosity modified number is the high number.
This is J300:
As you can see, there's only a kinematic viscosity
floor for the Winter grades, absolutely no upper boundary, so it's not a viscosity range like the hot grades. You still with me here?
So, let's look at that chunk you quoted:
multigrade oils are typically created by blending a low-viscosity base oil with VI improver additives (see the additives section of this book). For example, when these polymer additives are blended in the correct proportion with an SAE 15W oil, the oil flows like an SAE 15W oil at low temperatures and like an SAE 40 oil at high temperatures. The result is an SAE 15W-40 viscosity grade oil
So, look at J300, how do we get a 15W oil? Well, it has to pass CCS of 7,000cP at -20C and MRV of 60,000cP at -25C, and, it has to have a minimum 100C visc of 5.6cP.
Back in like the land before time days you could buy a straight Winter rated engine oil, it had no hot grade, just a straight-up Winter rating on a monograde, so like an SAE 15W. Taking that at face value, looking at J300 we know it was 5.6cP or heavier and, if sold today, would have had to have passed those other two tests, correct? And it had no VII improvers, otherwise, it would have to be a multigrade. We also have absolutely no idea what its 100C visc was, other than the fact that it was above the minimum. These would have been very light Group I based oils.
Now, the problem with just adding VII improvers to the above Group I SAE 15W monograde we just discussed is that VII's don't only work when they are hot. They impact the oil at all temperatures, the effect is just lower at cooler temps. So, add enough VII to get our SAE 15W to be in the 40-grade range when hot (12.5 to 16.3cSt) and all of a sudden, it doesn't pass as a 15W anymore, so maybe we end up with a 20W-40 or 25W-40. Ewwww.
But let's get back to what you stated:
the base oil is the low number, the viscosity modified number is the high number.
Base oils aren't sold as a Winter grade, they are sold by the 100C visc. PAO 8 is labelled as such because it's 8 cSt @ 100C, it's not sold as a 5W. The number on the left is simply the Winter grade for the oil, which we know, has to be heavier than the number indicated in the low shear 100C min visc column in J300, and pass the CCS and MRV requirements. I'm sure you can see that an 8 or 10cSt PAO is significantly heavier than the 3.8cSt floor for the 5W Grade category, yes?
Now, base oil selection is indeed made based on the intended Winter grade the oil will be shooting for. But that base oil viscosity is not represented by that number; the base oil viscosity is not the oil's Winter grade. An 8cSt Group II base will not have the same Winter performance as an 8cSt PAO for example; they will not meet the same Winter rating. Ergo, you can't correlate an 8cSt base oil viscosity with the 5W Winter grade, or the 10W Winter grade or even the 15W Winter grade, depending on the quality and type of base oil we are discussing.
Let me give you an example:
I can blend up a 0W-20 using a 4cSt Group III base, let's say we are using Yubase4. That base, by itself could be labelled as a 0W, an SAE 8, or a 0W-8, because it's a monograde. We add a shot of VII and get the 100C visc up into the 6.9 to 9.3cSt range and we have our 0W-20.
I can also blend up a 0W-20 using a heavier 6cSt PAO base, let's say we are using SpectraSyn6. That base, by itself could be labelled as a 0W, an SAE 16 or a 0W-16, because it's a monograde. It takes a tiny dash of VII to bring that up from an SAE 16 to a 0W-20.
You can ALMOST get there with SpectraSyn 8, which just misses the CCS visc for 0W and ends up being a 5W, and is also an SAE 20. Blending 6 and 8, getting a 7, you could likely produce a 0W-20 monograde (so also an SAE 0W and SAE 20).
Follow? So the above, I've given you three VERY different base oil viscosities, all meet the same Winter grade requirements, but all have very different 100C viscosities. With our last example, there isn't even a viscosity modifier in play, because the oil meets both the Winter grade and SAE grade requirements without them.
I think I already linked you to Gokhan's spreadsheet:
But you can look at the estimated BO KV100 column to get an idea of the base oil viscosities and see that this number is all over the map and you'll see the same number for different Winter grades or even inversions.
Example:
- AMSOIL AME 15W-40 has a base oil viscosity of 9.86cSt
- AMSOIL ACD 10W-30 has a base oil viscosity of 10.61cSt and is also an SAE 30 because it has no VII.
So here you have a 15W-xx with a lower base oil viscosity than a 10W-xx that also doesn't even have any VII in it.
Is any of this helping?
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