Viscosity calculator not linear?

[AKhan87]

Well, it's quite possible you won't have a 0w-20 with your concoction, most likely it would be a 5w-20, worst case it may be a 10w-20. With a 100C visc of ~8cSt. You also don't know what the HTHS is going to be, but it may not be the 2.6 of a formal 0w-20/5w-20, it could be lower, like around 2.4-2.5, which is what matters to your bearings. Energy Conserving xW-30 oils tend to be on the low end of the HTHS scale, around the 3.0 mark, so if the 0w-16 is 2.3 and the 10w-30 is 3.0, you'll be around 2.45, which is below the 2.6 spec'd for the engine if it calls for a 0w-20/5w-20.

By the way thank you for this, now I’m concerned because I had some CarQuest Full Synthetic 0w16 (4 quarts) and Valvoline Synthetic Blend 5w30 (2.5 quarts) left over and I did the last oil change (~2,700 miles) with that concoction and the engine is back spec’d for 0w20, and I don’t seem to have the right HTHS currently.

I have ~1,500 miles to an even 60k miles and I could change the oil then, or it’s crucial I change now? What do you guys recommend?

This concoction reduced the VVT-I gear noise on cold starts to once since the oil change from before where the startup noise was every other cold start, this is the only reason I was going to consider using a combination of this concoction again.

What do you guys recommend?

Thank You in advance

 

[OVERKILL]

By the way thank you for this, now I’m concerned because I had some CarQuest Full Synthetic 0w16 (4 quarts) and Valvoline Synthetic Blend 5w30 (2.5 quarts) left over and I did the last oil change (~2,700 miles) with that concoction and the engine is back spec’d for 0w20, and I don’t seem to have the right HTHS currently.

I have ~1,500 miles to an even 60k miles and I could change the oil then, or it’s crucial I change now? What do you guys recommend?

This concoction reduced the VVT-I gear noise on cold starts to once since the oil change from before where the startup noise was every other cold start, this is the only reason I was going to consider using a combination of this concoction again.

What do you guys recommend?

Thank You in advance

I recommend using a fully formulated lubricant of the proper grade That's why you see two premium oils, in the proper grade, for the vehicles in my signature.

If you want a reason as to why the HTHS visc doesn't seem to go up to where you might expect it with KV100, it is how the oils are blended. A 0w-16 will use thin base oils with relatively little VII, because it doesn't need as much "padding" to get to its target KV100 and target HTHS. On the other hand, your typical Energy Conserving 10w-30 also starts out with pretty thin base oils, typically of lesser quality, and gets dosed with more VII in order to bring up the KV100, which in turn drags up the HTHS. If you blend an SAE30 with PAO to hit the same KV100 as the 10w-30 you are using it would have an HTHS closer to ~3.5cP (about the same as the Euro xW-30's that have a higher KV100) And in fact, a PAO-based SAE30 would pass the 10W-xx designation, so it could be labelled a 10w-30 or SAE30. The reason the HTHS is 0.5cP lower with our Energy Conserving example is because of the thinner base oils and VII used, this reduces the effective viscosity under shear (bearings) which is what the HTHS test tests for.

Thicker than the 10w-30 you are using, but here's a heavy duty 10w-30 (with a higher KV100) blended using Mobil's EHC Group II+ bases:

You can see it is a blend of 4.5cSt and 6.5cSt bases. The resultant product has a viscosity of 5.85cSt (thinner than the visc of your 0w-16). It is bumped up to 11.9 using VII polymer, which in turn is how we get our 3.5cP HTHS. This, as I'm sure you've noticed, is a fair bit heavier than the 10.5cSt of your Castrol Edge.

If we look at Redline 10w-30, which is pretty close to a straight grade, it's 11.4cSt, so thinner than our blend here, but still manages the 3.5cP HTHS. The same goes for AMSOIL Dominator 10w-30, 11.5cSt, HTHS of 3.6cP. These oils use significantly heavier base oils and no, or next to no VII.

So, when you add the 10w-30 to the 0w-16, the resultant KV100 is easily calculated and lands around xW-20 as planned. However, because of how the 10w-30 is formulated, the HTHS is lower.

Now, if you were using a 3.5cP HTHS 10w-30 like the Redline or AMSOIL ones I just mentioned, and 70% 0w-16, that appears (again, just using the calculator) to put you at 2.61cP for HTHS and your KV100 would be ~8.4cSt, smack-dab in the middle of your desired xW-20 range.

Now, all this said, we aren't actually running the HTHS test on these blends, so these aren't measured figures. However, we DO have the approximate figures for the products themselves and we are essentially just ratio-ing them.

Another data point, just to for fun:
Pennzoil Hybrid 0w-16:
KV40: 38.2cSt
KV100: 7.6cSt
VI: 172
KV150: 3.47 (calculated)
HTHS: ~2.3cP

If we look at the same figures for a PAO base oil, that won't shear:
XOM SpectraSyn 8
KV40: 48cSt
KV100: 8.0cSt
VI: 139
KV150: 3.44cSt (calculated)
HTHS: 2.58cP

So even though the PAO base oil has a lower KV150, because it doesn't have VII polymers in it to flatten out under the shear test, the HTHS is higher (and yes, that base oil passes the criteria for a 5w-20, lol).

Ultimately, this is why oils are fully formulated and tested products and why I don't recommend people play the mixing game at home, particularly when using application-specific products like these new 0w-8, 0w-12 and 0w-16 lubricants as a foundation in an engine that doesn't call for them. While engines are generally quite tolerant, I wouldn't want to be the person that recommends something that causes damage.

 

[Gokhan]

Was playing around with the Widman viscosity calculator, where you enter the cSt for two different oils, and input the percentage of each oil. I found that even when you have half of each oil, the resulting viscosity is not half of the two added together and divided by two. This is true of the 40c and 100c calculation. Why is this? I can only assume that something there isn’t linear but it doesn’t describe what/how.

I am surprised that no one was able to answer your simple question. If the ratio is 50%, it is the geometric average of the two viscosities, not an arithmetic average. That's because:

Widman uses the Arrhenius equation: n = n₁^x₁ × n₂^x₂

^ represents exponentiation: a^b = a raised to the power of b.
n = dynamic viscosity of the mix/blend
n₁ = dynamic viscosity of oil 1
n₂ = dynamic viscosity of oil 2
x₁ = fraction of oil 1 (between 0 and 1)
x₂ = fraction of oil 2 (between 0 and 1)
Note that x₁ + x₂ = 1.

Even though the Arrhenius equation is for the dynamic viscosity, it also works well for the kinematic viscosity.

So, for x₁ = x₂ = 0.5 (50%), you get n = √ (n₁ × n₂)

Calculator for viscosity mixing based on the Lederer - Roegiers equation

I just realized that the Widman viscosity-mixing calculator and similar calculators on the Internet are totally useless. They are very inaccurate. After some brief reading, it looks like the Lederer - Roegiers equation works well. The only caveat is that there is an adjustable parameter alpha...

bobistheoilguy.com

There is a slight deviation from the Arrhenius equation in the Widman's formula. Perhaps, they are trying to estimate the dynamic viscosity from the kinematic viscosity using the temperature, as the Arrhenius equation requires the dynamic viscosity. Perhaps, they are trying to incorporate an additional approximation, which may not even work that well. If you read my thread linked here, Lederer–Roegiers equation works much better, but it requires empirical testing to determine α.