Are there situations where the shear-down of VI improvers can actually help a machine, with respect to flow rates during cold weather operation?
Can Shearing be Beneficial?
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If thinner was better why would you not just start with a thinner weight?
Welcome to the thick vs thin debate.
Welcome to the thick vs thin debate.
I was thinking of using a certain 5w-40 during the summer and having it reduce its viscosity by the time the colder months came along (with no servicing required).
Triple_Se7en
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Let me see if I got this correctly.......
You want your oil to do the same thing my 7-11 Slurpee did, after spending 2-1/2 hours in a beverage tray inside my Special Education / Handicapped Childrens' School Bus?
Mine had an opposite effect. It lost viscosity as the temperature rose inside that plastic cup and I didn't need to drive a single mile.
Can Shearing be Beneficial?
Yes, sometimes it is absolutely necessary.
Farmhouse Guide
I’m talking about having the lubricant gradually transition from a 40-grade down to a 30-grade and timing that (roughly) with the change in seasons.
Is all shearing detrimental to an engine’s performance when another variable (ambient temperature) trends lower at the same time?
Is all shearing detrimental to an engine’s performance when another variable (ambient temperature) trends lower at the same time?
Oil doesn't know when it's fall or winter time to thin out. But in general if you start your oil run in spring it should shear down a bit by fall, winter. What that viscosity is going to be at that certain time periods is anyones guess unless you do a few UOA's to see the results of the viscosity.
Using a VII such as a 35SSI material will shear down over time and when the oil thickens which is what oils do, you will end up back where you started. You are not going to see much if any difference on the cold side. You will see the difference show up at 100C which is where you are relying on the VII to work.
David
David
Oil degrades and gets dirtier (mostly the latter) over time. The basic answer to this question is "no." But I keep looking at the original post, wondering if there is some deeper strategy being contemplated... like maybe the ultimate strategy for making oil last as long as possible. I would also reiterate that the changing seasons, and outside temperature have very little real-world relevance for choosing oil weight. There is capability for very, very cold starting situations, I suppose, but it is irrelevant to most people living in temperate zones.
Quite a bizarre theory...and practice.
No. Picking the right oil for the equipment and the temperature it will be operating at would be the better way to go. How would one know if the oil is shearing to the desired viscosity, and precisely when the temperature requires a thinner oil.
This is why I change the oil on seldom used vehicles in the spring-well, and the whole condensation thing!
The winter flow rate would likely get worse instead of better. VII polymers have much less impact on cold weather performance compared to the base oil, a reflection of their very high viscosity index. Shearing of operating temp viscosity will have less impact on cold temp viscosity. What will effect cold temp viscosity is oxidative thickening, something all base oils undergo as they are used, and this will nullify (to an extent) the oil's pour point depressants. The oil could show a 1-1.5 cSt viscosity loss @ 100°C but give a 2,000-3,000 cP worse result in MRV @ -35°C and not achieve as cold of temperature in pour point testing.
The only time the shearing action of VII is beneficial is in friction reduction. There's some basis to temporary shearing allowing for better friction coefficients, but in most applications where such friction reduction would be noticeable and beneficial (ie: high rpm racing engines), the detriment to film thickness isn't worth it, and you can achieve better friction reduction with different methods.
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Looking at the question theoretically and not taking into account real life changes to the oil caused by use, viscosity loss due to shear would probably result in loss of HTHS viscosity in addition to kinematic viscosity at 40 and 100°C. Looking at it from a more realistic perspective, in real life oil's oxidize but it's not just the base oils. Additives oxidize and loose their performance characteristics. Problems would include wear, corrosion, deposits and loss of low tempeature characteristics.
Plus "flow rates during cold weather operation" is not an issue as long as the oil can be pumped. Pick an oil with an appropriate winter rating and it will work. For the most part, thinner oils are never "better" as long as they can be pumped.
Oxidative thickening is happening at the same time, as is loading with contaminants... You're more likely to get worse winter performance while not getting extra hot viscosity
VI improvers are activated by heat so I would say the answer is there will be no improvement in cold weather flow.
"These additives are polymeric molecules that are sensitive to temperature. As the temperature increases, these molecules tend to stretch out. As the molecules stretch out, the fluid's internal friction will increase, causing the fluid to flow at a slower rate. Therefore, it will have a higher viscosity."
Understanding Viscosity Index Improvers
"Can you explain how to calculate the viscosity of a viscosity index improver? I can't do this on my viscometer. If I make a blend of 10 percent polymer in SN 150 base oil, how can I calculate this...
www.machinerylubrication.com
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