HTHS explanation

petrv · Mar 15, 2005

Could someone please explain me this example of HTHS comparing two oils?

Motul 300V Power 5w40:
Viscosity at 100C: 13.8 mm2/s
HTHS at 150C: 4.51 mPa*s

Castrol Formula RS 10w60:
Viscosity at 100C: 22.7 mm2/s
HTHS at 150C: 3.7 mPa*s

I understand that at 100C, the Motul is more "like water" than the Castrol one. How does the situaiton look at 150C? Does the higher HTHS of Motul mean that at 150C the Castrol is "more like water" than Motul, so it means that the Castrol looses his viscosity with temperature faster than Motul, even if it's viscosity at 100C is higher?

Can I compare the HTHS number directly between these two oils? Or for example HTHS=4 for 5w40 oil is not absolutely the same as HTHS=4 for 10w60 oil? Is the HTHS some absolute number or relative with the viscosity grade of the oil?

Are there any materials about HTHS, it's testing, comparison etc?

Sorry for such basic questions

FowVay · Mar 15, 2005

Keep in mind that the 100ºC viscosity is measured in centistokes and represents the Kinematic viscosity of the oil.

The HT/HS viscosity is measure in centipoise and represents the absolute viscosity (aka dynamic viscosity).

To learn the actual difference in these numbers then do a google search for kinematic viscosity and dynamic viscosity. You'll see the different mathematical formulas used to derive both numbers and then you'll see what the numbers actually represent.

You can compare the cst's and cP's of one multi-grade oil to another but you can't compare the cst's of one oil to the cP's of another. The oil density will play the key roll in distinguishing the fluids dynamic viscosities.

petrv · Mar 15, 2005

Thank you very much for explanation. So if I can compare HTHS between various oils, can I say that the Motul 5w40 with higher HTHS is better at 150C than the Castrol 10w60, so it will be more friendly to the bearings ?

haley10 · Mar 15, 2005

HT/HS @150°C is an absolute. The 5W-40 is simply more shear stable than the wide-spread of the 10W-60. The 5W-40 is more shear stable at higher temperatures as it probably uses few VII's (viscosity index improvers). The 10W-60 is beginning to shear at higher temperature.

Unless the 10W-60 is specifically recommended (BMW) for certain reasons, I would think the 5W-40 is better all the way around for most vehicles.

petrv · Mar 15, 2005

So if I have two motors: one is designed to run 5w40 and second to run 10w60. I let both motors run at high temperature with their required oils (Motul and Castrol). The motor with Castrol will be more stressed than the one with Motul?

haley10 · Mar 16, 2005

quote:

Originally posted by petrv:
So if I have two motors: one is designed to run 5w40 and second to run 10w60. I let both motors run at high temperature with their required oils (Motul and Castrol). The motor with Castrol will be more stressed than the one with Motul?

That would be a function of engine design. The one that spec'd. 10W-60 might have other design issues that lead them to require this viscosity in the normal temp. range (BMW to avoid certain issues). Either oil, both ACEA A3 should have adequate HT/HS. Beyond what is required doesn't result in less wear.

Dr. T · Mar 16, 2005

You have to be joking...the HT/HS for the Castrol R 10-60 is more like 5.4 or 5.6 (from memory). Check GER or AUS websites for confirmation....

teamDFL · Mar 16, 2005

5.7 from Castrol Italia.

haley10 · Mar 16, 2005

5.4 @ 150°C from Australia web-site for the RS 10W-60. Maybe his data is from something other than the synthetic RS formula??

[ March 16, 2005, 03:25 PM: Message edited by: haley10 ]

MGBV8 · Mar 16, 2005

Its 3.7 on UK data sheet but must be a typo

427Z06 · Mar 16, 2005

quote:

Originally posted by petrv:
Are there any materials about HTHS, it's testing, comparison etc?

Sorry for such basic questions

Doing a search and reading up on the the methods used to make such measurements is the ideal way to learn.

However, I have a simple way I like to think about the difference in "cSt @100C" and "HTHS @150C".

Since the density is roughly the same for the oils in consideration, "cSt @100C" is the resistance to flow through oil passages in your engine, while "HTHS @150C" is the resistance to flow between surfaces with a very small clearance between them, e.g., main/rod bearings, lifters and cams, pistons and the cylinder wall, etc.

Hope that helps. (Triple flame suit on.)

Jay · Mar 16, 2005

quote:

Originally posted by petrv:

I understand that at 100C, the Motul is more "like water" than the Castrol one. How does the situaiton look at 150C? Does the higher HTHS of Motul mean that at 150C the Castrol is "more like water" than Motul, so it means that the Castrol looses his viscosity with temperature faster than Motul, even if it's viscosity at 100C is higher?

Can I compare the HTHS number directly between these two oils? Or for example HTHS=4 for 5w40 oil is not absolutely the same as HTHS=4 for 10w60 oil? Is the HTHS some absolute number or relative with the viscosity grade of the oil?

Are there any materials about HTHS, it's testing, comparison etc?

HTHS is dynamic viscosity, and dynamic viscosity is measured by dragging one surface (like a flat plate) over another surface (like another flat plate) with an oil film in between. The faster the plates move over one another, the higher the shear rate. HTHS is a high-shear rate, high temperature test that more closely approximates actual stress an oil encounters in a working engine than kinematic viscosity. So, HTHS viscosity is a better measure of viscosity under working conditions than kinematic viscosity. (Unless you're interested in how fast the oil will drain into the sump.)

petrv · Mar 16, 2005

quote:

Originally posted by Dr. T:
You have to be joking...the HT/HS for the Castrol R 10-60 is more like 5.4 or 5.6 (from memory). Check GER or AUS websites for confirmation....

Sorry

I took it from UK website, so let's considfer this some virtual 10w60 oil.

petrv · Mar 16, 2005

quote:

Originally posted by Jay:
HTHS is dynamic viscosity, and dynamic viscosity is measured by dragging one surface (like a flat plate) over another surface (like another flat plate) with an oil film in between. The faster the plates move over one another, the higher the shear rate. HTHS is a high-shear rate, high temperature test that more closely approximates actual stress an oil encounters in a working engine than kinematic viscosity. So, HTHS viscosity is a better measure of viscosity under working conditions than kinematic viscosity. (Unless you're interested in how fast the oil will drain into the sump.)

Thanks. So I assume that during the HTHS test, they set the clearence between the two surfaces, they heat the oil to 150C and move one surface over another with some defined speed and measure the force needed to move the plate? If so, higher force means higher HTHS? Is higher HTHS always better, i.e. I should choose the grade (5w40 in my case) and I should always look for oil with the highest HTHS?

MGBV8 · Mar 17, 2005

The German Castrol 10W60 is also 3.7 but Australia 5.4

http://129.35.64.91/bpglis/lubtds.nsf/technicaldata/223BC016BC0119B080256DB4004F260B?OpenDocument

Any expanation?

Jay · Mar 17, 2005

quote:

Originally posted by petrv:

So I assume that during the HTHS test, they set the clearence between the two surfaces, they heat the oil to 150C and move one surface over another with some defined speed and measure the force needed to move the plate? If so, higher force means higher HTHS? Is higher HTHS always better, i.e. I should choose the grade (5w40 in my case) and I should always look for oil with the highest HTHS?

Yes, for the most part, that's how it works. It can also be measured by squirting hot oil through an injector and measuring the force needed.

Higher HTHS isn't better. It's only higher. Just like higher kinematic viscosity isn't better, it's only higher. Higher HTHS means more viscous drag, less power, more heat, poorer fuel economy, and higher emissions; so you should choose the lowest HTHS that still provides good protection. Use your owner's manual as a starting point.

teamDFL · Mar 17, 2005

quote:

Originally posted by Jay:
Higher HTHS isn't better. It's only higher. Just like higher kinematic viscosity isn't better, it's only higher. Higher HTHS means more viscous drag, less power, more heat, poorer fuel economy, and higher emissions; so you should choose the lowest HTHS that still provides good protection. Use your owner's manual as a starting point.

quote:

Originally posted by haley10:
HT/HS @150°C is an absolute. The 5W-40 is simply more shear stable than the wide-spread of the 10W-60. The 5W-40 is more shear stable at higher temperatures as it probably uses few VII's (viscosity index improvers). The 10W-60 is beginning to shear at higher temperature.

Can someone please reconcile these too statements. It seems that if an HTHS is directly related to shear stability, then it is more than just a higher number and more drag on the engine.

Dr. T · Mar 17, 2005

Jay, that's good rhetoric it's just that one owner's manual for the same car says something different than an owner's manual for the same car in a different continent!

A higher HT/HS is of course, better. The question becomes whether you need it or not. For eg., a low hp cool running pushrod V-6 eg. Buick, probably doesn't need anything above a 2.99 HT/HS 5W-30 whereas a high revving/high hp engine should have more protection afforded by a higher viscosity. Generally, viscosity and HT/HS are coincident.

moribundman · Mar 17, 2005

Anybody remember those tests that said that with increasing HTHS wear decreased, but only disproportionally and that at some point the gains were negligible or non-existant? That point was reached at HTHS 3.5, which is why this figure is often one criterium for various engine maker's minimum oil requirements.

It seems reasonable to expect that for every engine, there will be a maximum HTHS that affords the best wear protection. It is also reasonable to expect that increased HTHS beyond some unknown point will be detrimental, most likely due to diminished oil flow.

Best, fastest, oil flow coupled with a high HTHS should offer the best compromise and protection.

Jay · Mar 17, 2005

quote:

Originally posted by teamDFL:

quote:

Originally posted by Jay:
Higher HTHS isn't better. It's only higher. Just like higher kinematic viscosity isn't better, it's only higher. Higher HTHS means more viscous drag, less power, more heat, poorer fuel economy, and higher emissions; so you should choose the lowest HTHS that still provides good protection. Use your owner's manual as a starting point.

Click to expand...

quote:

Originally posted by haley10:
HT/HS @150°C is an absolute. The 5W-40 is simply more shear stable than the wide-spread of the 10W-60. The 5W-40 is more shear stable at higher temperatures as it probably uses few VII's (viscosity index improvers). The 10W-60 is beginning to shear at higher temperature.

Click to expand...

Can someone please reconcile these too statements. It seems that if an HTHS is directly related to shear stability, then it is more than just a higher number and more drag on the engine.

I'll try. Shear stability has two meanings: there is a temporary shear that occurs when oil is under stress--the oil actually squishes and thins under compression, but recovers when the stress is released. Then there is permanent shear that occurs when the long-chain molecules are actually cut, and the oil permanently thins.

Oils with very high viscosity indexes generally, but not always, tend to be more prone to temporary and permanent shearing than oils with low VIs.

All things being equal, a 0w-30 will be thinner than a 10w-30 in actual use in an engine. This is certainly true of M1 0w-30(HTHS 2.99cP) vs 10w-30 (HTHS 3.17cP). If you could accurately measure it, you'd see slightly better gas mileage with the 0w-30, even though the 0w-30 has slightly higher kinematic viscosity than the 10w-30. 2.99cP represents less viscous drag than 3.17cP.

Is M1 0w-30 less shear-stable (in regards to permanent shearing) than M1 10w-30? Possibly, I don't know. They're both very shear-stable oils. Is M1 0w-40 (HTHS 3.6cP?) more shear-stable than M1 0w-20 (HTHS 2.6cP)? A thousand times no!

[ March 17, 2005, 11:29 PM: Message edited by: Jay ]

HTHS explanation

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