HT/HS number

Jeffrey Behr · Feb 4, 2004

I agree with Dr. T--it's a combination of base-oil viscosity AND quality and VI additives. Thicker base oils have higher H-T shear strength, LESS VI improver generates higher ratings, higher-quality base oil has higher HTHS, and I suppose there's some additive that improves HTHS.

I believe the presence of (more?) VI improvers in Castrol 0-40 versus 5-40 causes the significant reduction Dr. T quoted, altho the presence of some VI improver in Red Line's 5W-40 versus none in their 10W-40 affects their HTHS quality virtually not at all. (The 0.1 decrease from that of the latter to that of the former is only 2% and is statistically insignificant.) Maybe RL is using a VI improver with higher HTHS compared with the VII others use.

MolaKule · Feb 4, 2004

Reference this thread for background information:

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=21;t=000045

buster · Feb 5, 2004

This link by Molekule is excellent and should be read.

quote:

I don't evaluate an oil based on spec. sheet HT/HS and VI values alone. It can be misleading. Higher isn't always better

I agree entirely with haley10. I'd like to have A3, but an oil like M1 10w-30 with a HT/HS of 3.3 is as good as any. This oil never budges. Oils like M1 0w-40 or even Amsoil 10w-40 always thin out initially. The HT/HS is not the only spec to go by, obviously.

Colorado · Feb 5, 2004

Is the ht/hs value correlate to a better base oil, or better additive package? What affects this value the most?

TallPaul · Feb 5, 2004

I think it would be directly related to the viscosity of the base oil. The API Engine Oil Classifications chart for 2002 indicates a High-Sheer-Rate Viscosity (c) at 150C min of

2.6 for a SAE 20 oil

2.9 for SAE 30 and for some SAE 40 (0w-40, 5w-40, 10,w40)

3.7 for other SAE 40s (15w40, 20w40, 25w40, and 40) along with SAE 50 and 60.

So, I would surmise for example, that a 15w40 has a thicker base oil than a 10w40 since the 15w40 has the higher high sheer viscosity.

[ February 05, 2004, 12:27 PM: Message edited by: TallPaul ]

haley10 · Feb 5, 2004

Higher viscosity oils will always have a higher HT/HS. It generally follows viscosity.

Some oils use VI improvers that shear rapidly. Some spec. sheet HT/HS numbers look great, but the oil will have a much lower HT/HS very quickly.

I'd say basestock quality is paramount to being shear stable and maintaining viscosity.

I don't evaluate an oil based on spec. sheet HT/HS and VI values alone. It can be misleading. Higher isn't always better

Dr. T · Feb 5, 2004

I think it's both. That's why you can have one 30 weight A3 and another not. Addatives can increase the HT/HS.

Furthermore, I've never seen a non-synth. 30 weight listed as A3 no matter what viscosity it is on the scale. The synthetic base oil is better.

Likewise, the viscosity spread makes a difference. For eg. Castrol Syntec 5-40 is said to have a HT/HS of 4.5, while the Castrol R 0-40 is at 3.6.

Don't know which of the 3 makes the most difference. From what I've seen, it's probably viscosity of the higher number...most 40 and 50 weights seem to be able to get above 3.5

haley10 · Feb 5, 2004

Yep, good link Buster. I'm starting to like M1 10W-30 the more I run it.

heyjay · Feb 6, 2004

I thought Mobil 1 SuperSyn 10W-30 had a HTHS of 3.17 mPa s @ 150 C?

THis is one of the few specs I've been able to find from Mobil's web site, the other being kinematic viscosity at 40/100 C, flash point, and pour point.

I run the Mobil 1 10W-30 in summer, seems to hold up well.

Jerry

haley10 · Feb 6, 2004

quote:

Originally posted by heyjay:
I thought Mobil 1 SuperSyn 10W-30 had a HTHS of 3.17 mPa s @ 150 C?

THis is one of the few specs I've been able to find from Mobil's web site, the other being kinematic viscosity at 40/100 C, flash point, and pour point.

I run the Mobil 1 10W-30 in summer, seems to hold up well.

Jerry

Yep, that the number Mobil publishes. I also see some TBN values given that are much higher than Mobil specs.

buster · Feb 26, 2004

Z06 - Mobil 1 5w-30

Here is why I don't put to much stock into HT/HS alone. For long drains, it is more of a concern I imagine. I'd like the A3 rating, but the point is, it doesn't really seem to matter that much as we've seen.

[ February 26, 2004, 09:16 PM: Message edited by: buster ]

Jelly · Feb 26, 2004

Buster,

By no means will you see me make a "blanket statement" like that, as the importance of HT/HS depends on what kind of engine we are talking about.

A Z06 small block...probably not.
An ISX Cummins...yes.
Or an aftermarket gas engine running much higher valve spring pressures and higher camshaft loads as well...probably yes.

[ February 26, 2004, 09:21 PM: Message edited by: Jelly ]

HT/HS number

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