Explain the HTHS/Viscosity at 100c relationship to me

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Patman

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How come some oils don't do as well on the HTHS test than you'd think, based on their viscosity at 100c? Here's an example: if you compare two versions of Mobil 1 ESP Formula, the new 0w40 that is factory fill on 2019 Corvettes, and their 5w40, the two oils both have a viscosity at 100c that is not that far off (12.9 vs 13.4) but yet the HTHS of the 5w40 is significantly higher, at 3.8, compared to 3.53 for the 0w40. And by the same token, the 5w30 ESP Formula I'm using has a slightly higher HTHS of 3.58, even though it's viscosity at 100c is lower than the 0w40 (12.1 vs 12.9) What is causing the 0w40 to slightly underperform in the HTHS test compared to the other choices? Is it a different base stock? Less VII?
 
Originally Posted by OVERKILL
Lighter base oils and more VII.


So to expand on that a little bit more, would that mean the 0w40 would see it's HTHS drop even more in use than the other choices would? (once those viscosity index improvers start to break down)
 
Originally Posted by Patman
How come some oils don't do as well on the HTHS test than you'd think, based on their viscosity at 100c? Here's an example: if you compare two versions of Mobil 1 ESP Formula, the new 0w40 that is factory fill on 2019 Corvettes, and their 5w40, the two oils both have a viscosity at 100c that is not that far off (12.9 vs 13.4) but yet the HTHS of the 5w40 is significantly higher, at 3.8, compared to 3.53 for the 0w40. And by the same token, the 5w30 ESP Formula I'm using has a slightly higher HTHS of 3.58, even though it's viscosity at 100c is lower than the 0w40 (12.1 vs 12.9) What is causing the 0w40 to slightly underperform in the HTHS test compared to the other choices? Is it a different base stock? Less VII?


https://mobiloil.com/en/motor-oils/mobil-1/mobil-1-esp

Your 5W-30 ESP of KV100 = 12.1 doesn't match with Mobil's spec info - I see 11.8 cSt. And I don't see HTHS = 3.58 for their 5W-30 ESP but rather 3.5.

I see:

Mobil ESP 0W-40
KV40 = 69
KV100 =12.9
HTHS = 3.53

Mobil ESP 5W-40
KV40 = 81
KV100 = 13.4
HTHS = 3.8

Mobil ESP 5W-30
KV40 = 62.6
KV100 = 11.8
HTHS = 3.5

Anyway, what I see just comparing KV100 to HTHS (and with others oils besides these 3) is that HTHS is typically higher with a higher KV100. There might be a rare instance when that's not true if you look hard enough.

IMO, all three of those oils have plenty of HTHS to insure wear protection.
 
There was an old thread where someone collected KV100 and HTHS data. I don't recall the thread, but I'll see if I can get the raw data and come up with a plot ... will post later if I can.
 
Under perform is relative, metal protection versus fuel economy. Nowadays low hths is a "good" feature. There is another way to look at 0w40's, they really are 5w30's most of their life in the engine and because they start as 40 weights they don't have the same rules to get certified because they consider them to be HD oils. Most specs are now 20 and 30 weights due to the epa hamstringing manu's on mileage.
 
Originally Posted by ZeeOSix
There was an old thread where someone collected KV100 and HTHS data. I don't recall the thread, but I'll see if I can get the raw data and come up with a plot ... will post later if I can.


Cool! Generally speaking the HTHS and viscosity at 100c seem to track in step, but there are instances where it doesn't seem to make as much sense.
 
Originally Posted by Patman
Originally Posted by OVERKILL
Lighter base oils and more VII.


So to expand on that a little bit more, would that mean the 0w40 would see it's HTHS drop even more in use than the other choices would? (once those viscosity index improvers start to break down)


Not necessarily if high quality VII's are used and a significant dose of PAO or GTL is used as the base, which would reduce the amount of VII required. Castrol 5w-40 for example, was/is an inferior lube to their 0w-30/0w-40 based on base oil and certifications.

0w-40's are generally blended light and tend to hit around the 3.5-3.6 range for HTHS unless it's an HDEO. The 3.5 is the minimum for a few of the Euro approvals and ACEA classifications, so that's why you see most of them at around that point.
 
You can tell what manu's are using 0w40 like a 30 weight if they are on the low end of the viscosity, if it is in the 12's it will be a 5w30 after shearing down. Strictly talking your average run of the mill group 3.
 
Generally, the larger the viscosity-spread, the lower the HTHS is for a given KV100. This is due to increased VII used in high viscosity-spread oils that temporarily shears in a HTHS environment.
 
Last edited:
Originally Posted by Patman
Originally Posted by ZeeOSix
There was an old thread where someone collected KV100 and HTHS data. I don't recall the thread, but I'll see if I can get the raw data and come up with a plot ... will post later if I can.

Cool! Generally speaking the HTHS and viscosity at 100c seem to track in step, but there are instances where it doesn't seem to make as much sense.


Here you go ... you can see the trend, but yes there are some cases where it's not a perfect correlation. But generally speaking a higher KV100 will also give a higher HTHS. Of course having the official specs on the specific oil is what you want to go by.

Here's where the raw data came from: https://www.bobistheoilguy.com/foru...hs-influence-on-oil-pressure#Post4717505

KV100 vs HTHS.JPG
 
I plotted the 4 Mobil ESP oils ... and you can see the 0W-40 falls out of the trend of the others. So this is a case where it's not a solid correlation between KV100 vs HTHS.

Mobil ESP - KV100 vs HSHS.JPG
 
Apples and oranges.
You're looking at two independent measures of viscosity and HTHS generally trumps kinematic viscosity where it matters.
In a hard run engine you probably want at least 3.5 HTHS and the SAE grades that will provide that include at least one 0W-30.
 
Originally Posted by fdcg27
Apples and oranges.
You're looking at two independent measures of viscosity and HTHS generally trumps kinematic viscosity where it matters.
In a hard run engine you probably want at least 3.5 HTHS and the SAE grades that will provide that include at least one 0W-30.


Doesn't matter if they are different measures of viscosity. It's still a comparison of the correlation between KV100 and HTHS. They don't have to be in the same units to make that type of correlation.

And of course the HTHS spec is the one to go by if you're worried about engine protection under extreme conditions. I'm not implying it's not. But if all you had was the KV100 and not any HTHS info to go by, then choosing a thicker oil (higher KV100) will typically give you better HTHS.
 
There's quite a few 30 grade pcmos that have greater than 3.5 here in oz...

Dex 2 is a common recommendation for gm petroleum or diesel cars

20180916_103301.jpg
 
I'll repeat the key point already stated: it is due to temporary shear thinning...temporary viscosity loss at high shear rate. It regains its viscosity when the shear stress goes away. A Newtonian fluid does not have a shear thinning behavior since its viscosity does not vary with shear rate. To be Newtonian, polymer VIIs must NOT be present. Having "shear stable" VIIs does not change that. "Shear stable" VIIs refers to how well they avoid permanent viscosity loss, not temporary loss.
 
Originally Posted by burla
You can tell what manu's are using 0w40 like a 30 weight if they are on the low end of the viscosity, if it is in the 12's it will be a 5w30 after shearing down. Strictly talking your average run of the mill group 3.
A thick 30 instead of the bottom end of the 30 scale.
 
I suspect the primary reason for this behavior is the type of VII used. Although it's not an absolute certainty, the 5W30 & 5W40 are likely to use OCP VII (Olefin CoPolymer). These have relatively poor cold flow (as in CCS) properties but are pretty robust in terms of HTHS.

Because of their poor cold flow properties, it's virtually impossible to make a 0W40 with OCP so you're forced to using expensive HSD VIIs (Hydrogenated Styrene Diene). Although these have far superior CCS performance, they are relatively poor in terms of HTHS.
 
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