Viscosity Index - what does it mean?

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Melbourne, Australia
I used to think that the higher the VI the better but someone told me otherwise, can any bros here pls enlighten me, thanks. The msg below are the answer by a fellow forumer. If you compare 10w30s, the one with the lower VI is the better choice. Less VI improvers mean the oil has a less chance to shear with VII breakdown. Look at specs for M1 10w30, Redline 10w30, RP 10w30 and compare with Chemlube. Furthermore, why is there no website for chemlube where specs are available. No one in bobistheoilguy forums even talks about chemlube. Cant be a very popular oil in the states.
 
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Ephraim
quote:
Originally posted by Trex101: I used to think that the higher the VI the better but someone told me otherwise, can any bros here pls enlighten me, thanks. The msg below are the answer by a fellow forumer. -*-*
Copy from the main Web Page link: VI (Viscosity Index) An arbitrary scale used to show the magnitude of viscosity changes in lubricating oils with changes in temperature. Oils with low VI number such as VI=0 ("zero") have high dependence of viscosity change on temperature. They thicken quickly with decreasing temperature, and thin out quickly with increasing temperature. Oils with high VI number such as VI=200, will still thicken with decreasing temperature but not as rapidly, and also will thin out with increasing temperature, but again not as much as low VI oil. VI number can also be "negative" Tables found in ASTM Method D 2270 are widely used to determine VI number. However, VI does not tell the whole story -- it only reflects the viscosity/temperature relationship between temperatures of 40°C and 100°C. Two lubricants or base oils with the same VI number may perform dramatically different at low temperatures in the -5°C to - 50°C range. " viscosity The measure of the internal friction or the resistance to flow a liquid. Low viscosity fluids flow easily (water); High viscosity fluids pour slowly (molasses). Viscosity Index Improver (VII) Chemical additive that is added to finished lubricants to improve the viscosity index (see above). While Viscosity Index Improvers can enhance VI, they can break down under shear or over time, resulting in diminished performance. " ---------- Maybe the last part of this is why they refered to it the way they do. VII's improve the tackiness of the oil. Some applications or service are just demanding on an engine and their oil, and this is just another way to protect. I am using an OIL with a VI of 150 (right now) and have oil burn on a 10w-30, my truck has never liked them since new, and even now doesn't care for them. I have and do use Oils with a LOW VI, and I still have gotten 15-20-30K without much thinning or thickening. I have also used the same oils that I have added a lot of VII to and 1. reduced my oil consumption and 2. stayed stable longer... So I guess this can be dependant on the VII and other factors I know noting about. VII's are usually or perhaps always a Polymer, and usually blends with many types of oil SYN and Dino. It improves the "BODY" or texture or Viscosity of the oil "TO SOLVE A PROBLEM", so in otherwords it's used Where it will HELP. I believe that the VII's MIX complete with the oil it is added to and thus BECOME ONE (like Star Wars) with the oil (FORCE LUKE). VII's Do reduce NOISE, I know when I add them in my oil, my ticking gets much lighter, and engine sounds less stressed when I put the peddle to the Metal. They also I believe in ALL but the most brutal applications, always maintain a BETTER FILM strength... Since I do a lot of stop and go, and often Extended Idle, not to mention the above, I like this part too. They will also help reduce leaks in some respects... I have added them to an oil leaking through the seals many times, and reduced or dtopped leaks here (better IMHO in HYDRAULIC systems like power steering). It also helps lower the pour point; thus in some cased (oil dependant) you can add one to say a 10w oil and actually have a lower POUR than a 20w, this I also liked because I had been runnind a straight 30W, thus kinda making a multi outa it, someone I'm sure will correct me if I'm wrong, but this is my understanding... I do know it's easier to start in the cold cold with the one I use in there. Thus it also improves the top end temp performance as well, so this is where I see the benefit almost ALL the time because in Houston, Tex. it is usually like summer most of the year, and I get better running engine when it's HOT. And since it thickens and clings to metal better, there is more oil film upon NEW STARTS, which I do a lot (20-60 times a day when busy), so thus the BERINGS have improved fluid film lubrication (another reason why I add it to my SEVERE application - courier work). It does TAKE-AWAY per se from the Oils additive package, and does not help clean or protect in this way but has other benefits I'm sure I'm not saying or even aware of at the moment. VII's do work in new and old, but perhaps work better in the old because it helps them go longer with less $$$$, it should be noted, that if you plan on using them it would be best to have a clean engine and never add to dirty oil. When I add them I do so to a HOT engine because they are so thick, and then I let it run a little while. Some VII's are plain or naked and others are not; try to find one with things that help boost other things like fighting acids or clenaning ability. Whatever you do, don't add too much, and IMO from experience, when you do BOOST it with a VII, it can take several oil changes unless you do a flush and rinse to get ALL of it out.
 
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1,533
Location
Ephraim
quote:
Originally posted by Trex101: Ok, one more question. So which is the better oil RP 5W30 with VI:161 or RP 10W30 VI:141
I'm not sure. From what I know about oil, I'd say generally the 10w-30. But if you have an application that takes the 5-30 then youre suppose to do that. Me, I don't believe everything I'm told. I would pick the 10-30 and keep the OCI's short 3-4K
 

Al

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19,154
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Elizabethtown, Pa
Maybe here is your confusion: Less VI Improver is better because it is what shears down and thins out the oil....but...Higher VI (viscosity index) of the base stock is good bc it implies less viscosity change with temperature. But in the final analysis, VI (viscosity index) is pretty much of a useless arbitrary number [Smile] .
 
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1,533
Location
Ephraim
quote:
Originally posted by Al: -*-* But in the final analysis, VI (viscosity index) is pretty much of a useless arbitrary number [Smile] .
I would not say useless, but not a major factor to be concerned with in most applications.
 
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1,533
Location
Ephraim
quote:
Originally posted by Al: Maybe here is your confusion: Less VI Improver is better because it is what shears down and thins out the oil....-*-*
So what's your take on VII added to the oil as an additive like I do?
 
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2,556
Location
Columbus Ohio
quote:
Originally posted by Trex101: Ok, one more question. So which is the better oil RP 5W30 with VI:161 or RP 10W30 VI:141
Unless you are running in very low temps (below 0), then use the RP 10w30.
 
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