What happens to HTHS when the oil shears down?

[vinu_neuro]

I don't suppose anyone knows this (maybe one of our resident tribologists or chemists does), never seen in a UOA.

What's the relationship between 100C visc drop (from shearing down) and that effect on hths? Does hths drop by the same %?

I'm very seriously looking at M1 0W-40 for it's hths performance, and uoa's indicate it usually shears out of grade (sometimes extremely). It does thicken back up, but I very highly doubt oxidative thickening improves hths!

 

[JAG]

Studies have shown that the % drop in HTHS is usually roughly 50% of the drop in kinematic viscosity at 100C.

 

[CATERHAM]

The relationship between KV100 and HTHS vis' is indeed an interesting one. Unlike KV100, HTHS vis correlates very closely with the operational viscosity in an engine and the proxy for operational viscosity is oil pressure.
If you have an OP gauge particularly in conjunction with a oil temp' gauge then you will be able to precisely monitor first hand any viscosity loss as the oil ages; no need to wait for a UOA which is not particularly accurate since it is a kinematic measure.

But on the assumption that you don't have oil gauges I will say that the M1 0W-40's latest formulation looks to be likely more shear stable, at least on paper. The oil is thicker to start with, with a higher HTHS vis of 3.8cP and the KV100 spec' has dropped to 13.5cSt. The lower KV100 relative to the higher HTHS vis is a good indication of the use of better base oils requiring less use of VII's and therefore less possibility of oil shear.
Of course if you want to eliminate the possibility of shear altogether then go with Red Line's 5w30 which contains no VII's and has the same HTHS vis of 3.8cP. Dispite it's even lower KV100 it actually has the same operational viscosity to M1's 0W-40.

 

[HangerHarley]

Originally Posted By: CATERHAM
The relationship between KV100 and HTHS vis' is indeed an interesting one. Unlike KV100, HTHS vis correlates very closely with the operational viscosity in an engine and the proxy for operational viscosity is oil pressure.
If you have an OP gauge particularly in conjunction with a oil temp' gauge then you will be able to precisely monitor first hand any viscosity loss as the oil ages; no need to wait for a UOA which is not particularly accurate since it is a kinematic measure.

But on the assumption that you don't have oil gauges I will say that the M1 0W-40's latest formulation looks to be likely more shear stable, at least on paper. The oil is thicker to start with, with a higher HTHS vis of 3.8cP and the KV100 spec' has dropped to 13.5cSt. The lower KV100 relative to the higher HTHS vis is a good indication of the use of better base oils requiring less use of VII's and therefore less possibility of oil shear.
Of course if you want to eliminate the possibility of shear altogether then go with Red Line's 5w30 which contains no VII's and has the same HTHS vis of 3.8cP. Dispite it's even lower KV100 it actually has the same operational viscosity to M1's 0W-40.


OK. So Oil Pressure gauge indicates lower Oil pressures consistently, its time to go about changing the Oil basically?

I also learned RL 5w30 contains no VII.. Thats amazing! And good! Yes? Any OTHER Oil contain Zero "Viscosity Index Improvers?"

 

[CATERHAM]

Originally Posted By: HangerHarley
Originally Posted By: CATERHAM



OK. So Oil Pressure gauge indicates lower Oil pressures consistently, its time to go about changing the Oil basically?

I also learned RL 5w30 contains no VII.. Thats amazing! And good! Yes? Any OTHER Oil contain Zero "Viscosity Index Improvers?"


Without a oil temp' gauge it's hard to say conclusively, but yes if the OP is consistently lower than the virgin oil then you've likely got viscosity loss due to shear and/or fuel dilution. If an oil change with the same oil restores the OP, you've got your answer.

A few of the better syn oils contain no VII's.
Of the top of my head, RL's, 0W-20,5W-20,5w30,10W-30 and 15w40.
Amsoil 0W-20
Fuchs Titan GT-1 OW-20
Many 10W-30 syn's contain little or no VII's.

 

[mitsuman47]

Originally Posted By: CATERHAM

A few of the better syn oils contain no VII's....Amsoil 0W-20.


So, I would assume this is a good thing. But, ASM only has a VI of 165. So, it makes me wonder what all the praise was about when we started seeing the VOA's come in on the honda and toyota 0w-20 oils. They have VI's in the low 200's, and everyone was ooohing and aaahing.

So, which is better? Do, the honda and toyota 0w-20 oils have VII's in them, thus making the VI numbers less impressive?

 

[CATERHAM]

It's not a matter of what is better. A very high VI is desirable but it does matter to some and to some applications how it done.

You can only achieve VI's up into the 160's without VII's through the exclusive use of GP IV & V base oils, so by def'n they're expensive and limited to the specialty suppliers. But if you want an oil that won't shear that's the way to go.

Amsoil 0W-20 is an older formulation. It has good extreme cold performance but it is actually a heavy 20wt with it's HTHS vis of 2.8cP. All manufacturer's that spec' a 20wt want a light oil with a HTHS vis of 2.6cP.

The car manufacturer's want high VI oil's that aren't too expensive and they are willing to accept some oil shear to get it. And that especially applies to the Toyota and Honda 0W-20's which are very light oils particularly at typical start-up temp's due to their very high VI's.