Say you have a standard 5w30 with 100C viscosity =10cSt and a HTHS of 3.0. If you run you OCI and it sheers to 9cSt. What is the relationship of that to HTHS mPa•s. If 100C viscosity drops 10%, then does HTHS mPa•s do the same so it is now 2.7 mPa•s. Knowing how oil behaves over temp, which is not linear, it got me wondering if this would not be linear.
Does HTHS go down linearly with 100C viscosity?
- Thread starter jstutz
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Depends on the VIIs (if any) and basestocks. Some oils will shear badly, others very little, others none at all.
My guess is that if the oil sheared and the VII were less active the HTHS would decrease slightly more than a linear amount to some limit. So if the it sheered from 10 cSt to 9 at 100C then maybe it would have a 2.6 cSt at 150C. My reasoning for this is that a straight 30 grade sometimes has a lower HTHS than virgin 5W30 due to viscosity index and VII, so the loss of VII activity might mean a nonlinear loss of HTHS (less viscosity index). But to tell you the truth I don't really know and maybe it would not lol. It's a good question.
The relationship for this when due to permanent mechanical shearing has been found to be: % drop in HTHS is roughly 1/2 of the % drop in KV @100C. Reference(s) are in some previous replies I've made in past threads on this subject.
Originally Posted By: JAG
The relationship for this when due to permanent mechanical shearing has been found to be: % drop in HTHS is roughly 1/2 of the % drop in KV @100C. Reference(s) are in some previous replies I've made in past threads on this subject.
If this is a case, pre-shearing oil can lead to lower 100C but higher HTHS than oil that came at the desired 100C vis? Does this explain why some oils have higher HTHS than others even with close to identical 100C vis?
The relationship for this when due to permanent mechanical shearing has been found to be: % drop in HTHS is roughly 1/2 of the % drop in KV @100C. Reference(s) are in some previous replies I've made in past threads on this subject.
If this is a case, pre-shearing oil can lead to lower 100C but higher HTHS than oil that came at the desired 100C vis? Does this explain why some oils have higher HTHS than others even with close to identical 100C vis?
Originally Posted By: JAG
The relationship for this when due to permanent mechanical shearing has been found to be: % drop in HTHS is roughly 1/2 of the % drop in KV @100C. Reference(s) are in some previous replies I've made in past threads on this subject.
Thanks man. Ill try to dig them up. If i find them, ill repost them here or link to your older posts.
The relationship for this when due to permanent mechanical shearing has been found to be: % drop in HTHS is roughly 1/2 of the % drop in KV @100C. Reference(s) are in some previous replies I've made in past threads on this subject.
Thanks man. Ill try to dig them up. If i find them, ill repost them here or link to your older posts.
Originally Posted By: sangyup81
Originally Posted By: JAG
The relationship for this when due to permanent mechanical shearing has been found to be: % drop in HTHS is roughly 1/2 of the % drop in KV @100C. Reference(s) are in some previous replies I've made in past threads on this subject.
If this is a case, pre-shearing oil can lead to lower 100C but higher HTHS than oil that came at the desired 100C vis? Does this explain why some oils have higher HTHS than others even with close to identical 100C vis?
Pre-shearing oil would just make it closer to being non-Newtonian and more like an oil without polymeric VIIs. Kinematic viscosity at 100C AND HTHS viscosity will go down. It's just that the percent drop in kinematic viscosity at 100C will be about twice the percent drop in HTHS, since the former test does not take into account temporary viscosity loss resulting from high-shear rates while HTHS does.
Oils that have higher HTHS than others even with close to identical 100C vis are that way because of having less polymeric VIIs and/or VIIs which allow less temporary viscosity loss.
Originally Posted By: JAG
The relationship for this when due to permanent mechanical shearing has been found to be: % drop in HTHS is roughly 1/2 of the % drop in KV @100C. Reference(s) are in some previous replies I've made in past threads on this subject.
If this is a case, pre-shearing oil can lead to lower 100C but higher HTHS than oil that came at the desired 100C vis? Does this explain why some oils have higher HTHS than others even with close to identical 100C vis?
Pre-shearing oil would just make it closer to being non-Newtonian and more like an oil without polymeric VIIs. Kinematic viscosity at 100C AND HTHS viscosity will go down. It's just that the percent drop in kinematic viscosity at 100C will be about twice the percent drop in HTHS, since the former test does not take into account temporary viscosity loss resulting from high-shear rates while HTHS does.
Oils that have higher HTHS than others even with close to identical 100C vis are that way because of having less polymeric VIIs and/or VIIs which allow less temporary viscosity loss.
Originally Posted By: webfors
It's been asked before on many a threads. I just can't remember what the consensus was.
http://www.bobistheoilguy.com/forums/ubb...590#Post2095590
It's been asked before on many a threads. I just can't remember what the consensus was.
http://www.bobistheoilguy.com/forums/ubb...590#Post2095590
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