Why we should love HTHS specs:

[ZeeOSix]

Thanks again, I see the reference to the Toyota work. Quite the article, written in English with graph labels in Russian, posted in a Russian website, referencing a 24 year old Japanese study.

Was HTHS different in 1997 ? HTHS is HTHS ... regardless of how old it is.

 

[jurko]

HTHS is important. But don't forget VI.
The oil with higher VI will change viscosity at lower rate based on the temperature.

For example all these SAE 5W-30 motor oils have HTHS ≥3.5
HTHS High/Low

If I had to choose though I'd go with oil which has higher VI.
VI High/Low

 

[ZeeOSix]

HTHS is the viscosity at 150C at a specific shear rate ... regardless of what the VI is of the oil. The amount of VI will have some effect on the HTHS, but the HTSH is still the HTHS of any specific oil regardless of the formulation or amount of VIIs An oil with a higher VI may actually shear down worse over time than one with a lower VI. IMO, an oil that retains the higher HTHS over the entire OCI is the better one.

 

[jurko]

HTHS is the viscosity at 150C at a specific shear rate ... regardless of what the VI is of the oil. The amount of VI will have some effect on the HTHS, but the HTSH is still the HTHS of any specific oil regardless of the formulation or amount of VIIs An oil with a higher VI may actually shear down worse over time than one with a lower VI. IMO, an oil that retains the higher HTHS over the entire OCI is the better one.

I've read a lot about motor oils and lubrication in a past few months and know little bit about it. But I am far from knowledgeable about what's involved and what ASTM test methods are applied and what's involved to determine the values of different oil properties. I was never a blender or worked in tribology R&D or testing.
I do have a degree in chemistry but with emphasis on metallurgy. Therefore I'll refer to THIS POST about HTHS and what it actually means..
The one thing I know about HTHS number is that that alone doesn't tell you everything. One has to take a look at the molecular structure of VM's and quality of base oil used.

 

[ZeeOSix]

^^^ I'm well aware of what HTHS viscosity is. And if you compared 100 different oil's HTHS regardless of the formulation, the one with the highest HTHS simply has the highest HTHS viscosity at time of testing.

However, if the shear rate is measured at higher shear rates than the normal standard, the oil with more shearible VIIs will most likely have a lower HTHS at the elevated shear rate. And as mentioned, an oil with more VIIs can potentially shear more with use, which would lower/hurt the HTHS viscosity.

 

[jurko]

Couldn't one also say that different engines affect shear rate differently and therefore OCI might be adjusted according to that?

 

[ZeeOSix]

Couldn't one also say that different engines affect shear rate differently and therefore OCI might be adjusted according to that?

Of course, every engine and their use conditions effect the shear level to some degree. High revs vs low, more cam chains vs not, 32 cam lobes vs 16, long OCI vs short, sump capacity, (ie, 4 vs 8 qt), etc.

But I'm talking about different oils in the same exact use conditions. The oil with more VIIs and a resulting higher VI may shear down more under the same exact use conditions. And as it shears, the KV100 and HTHS will also decrease.

 

[jurko]

The oil with more VIIs and a resulting higher VI may shear down more under the same exact use conditions. And as it shears, the KV100 and HTHS will also decrease.

Not necessarily always true. According to what I've read the VM's (VII) polymer molecules size and weight has lot to do with shear rate and not the quantity of VII.

 

[ZeeOSix]

Not necessarily always true. According to what I've read the VM's (VII) polymer molecules size and weight has lot to do with shear rate and not the quantity of VII.

I didn't say always ... I said may. So yeah, there are many factors involved. I just chose an oil with a relatively high HTHS which also doesn't have some crazy high VI. If you're super concerned about it, do some UOAs to see how it dilutes and shears with your use and go from there.

 

[jurko]

I didn't say always ... I said may. So yeah, there are many factors involved. I just chose an oil with a relatively high HTHS which also doesn't have some crazy high VI. If you're super concerned about it, do some UOAs to see how it dilutes and shears with your use and go from there.

Thanks for the conversation I learned something more about oil from it.
Cheers.

 

[kschachn]

All of which is predicated on the specific engine being one that promotes mechanical shear in the oil. We've seen very few demonstrated instances of that happening here on Bitog.

Also this discussion is being based on some contrived formula not actual ASTM tests or results.

 

[ZeeOSix]

Viscosity Matters - as well as HTHS.

http://www.lube-media.com/wp-content/uploads/Viscosity-matters-WEB-ONLY-Sept19c_FINAL.pdf

 

[ofelas]

An informative article, enjoyed it, thx.

Viscosity Matters - as well as HTHS.

http://www.lube-media.com/wp-content/uploads/Viscosity-matters-WEB-ONLY-Sept19c_FINAL.pdf

 

[KCJeep]

I read somewhere, but I don't recall now where probably here, that HTHS decline is at about half the rate of cSt@100 shear.

 

[Silver]

Plenty of people are having chain issues with the OEM spec'd oil and change interval. Plenty. Not to mention a rash of low tension piston rings that fail to seal, along with clogged piston oil drain holes.

What's causing the clogged drain holes?

 

[Jonas]

HTHS >3.0 for the win.

Look at the graph below and compare it to the wear graph shown in the article. See the similarity on ring wear as a function of HTHS. The hot running ring pack area doesn't seem to like low HTHS oil.

View attachment 49975

View attachment 49977

According to the top graph, it seems 2.6 HTHS has the least wear at low RPMs?

 

[ZeeOSix]

According to the top graph, it seems 2.6 HTHS has the least wear at low RPMs?

Yeah, looks like 2000 RPM and below the HTHS doesn't matter. Probably another reason car manufactures specify thicker oil for extended RPM use - racing, high speed highway driving, etc.

 

[demarpaint]

Yeah, looks like 2000 RPM and below the HTHS doesn't matter. Probably another reason car manufactures specify thicker oil for extended RPM use - racing, high speed highway driving, etc.

If that's the case then running 0W30 or 5W30 in both my Jeeps especially the 4.10 geared Wrangler was the way to go, instead of the 5w20 stamped on the fill caps. Most of the time when I'm driving it is cursing over 2,000 rpms.

 

[Jetronic]

don't forget that fuel dilution has just as big an impact on HTHS as it does on KV, unlike permanent VM shear. And fuel dilution is possibly a much more prevalent problem than mechanical shear these days.

 

[Hogwash]

What would one define as "high speed driving"? I do a lot of highway commuting in my 4.0 Tacoma. And at 70 MPH I'm turning about 2100 RPM....which doesn't seem like much to me.

It would seem that RPM would play as much of a role, if not more, than actual vehicle speed.

I plan to go with either Valvoline synthetic Maxlife 5/30 or 10/30 with my next OC. They are at 3.2 and 3.3 respectively. That would seem sufficient according to what some are saying