Would like an explanation of this term. For instance Red Line 5w30 says the viscosity index is 162 I believe, while the the Red Line 10w30 says the viscosity index is 142. What is the better number, and why. Thanks in advance guys.
Viscosity Index....What does it mean?
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It's the absolute measure of viscosity for a given weight of oil as I understand it.
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How much it changes between 40C and 100C. The more it changes, the lower the index. Synthetics thin less when cooled and thicken less when heated. They have broader VI.
Gary...Thank you,just so I make sure I am understanding. In the RL numbers I provided, 5w30 thins and thickens more? Given the RL numbers then, is the 10w30 oil more, how shall I say it...stable?
Nah the 10w30 is less stable, it is less often where you want it! Look at the front page of this site for the viscosity charts, your bearings generally like 5-100 cSt and the 10w30 provides this over a narrower temp range.
In the old days multigrades used to shear down and people got 10w30 over 5w30 b/c 10 was the "worst" it could get.
Also read up on viscosity index improvers (polymers etc), a not very durable additive, syns get by with few to none.
In the old days multigrades used to shear down and people got 10w30 over 5w30 b/c 10 was the "worst" it could get.
Also read up on viscosity index improvers (polymers etc), a not very durable additive, syns get by with few to none.
In layman's terms it's an oil's resistance to thinning or thickening with changes in temperature.
The higher the number the better.
Syn oil's have inherently higher VI's than mineral oil without the addition of polymer viscosity index improvers (VII's)which can shear under heat and pressure.
In the RL example you've given, neither the 5w30 nor the 10w30 oil's contain any VII's, consiquently I'd say the 5w30 is the better oil due to it's higher VI.
The higher the number the better.
Syn oil's have inherently higher VI's than mineral oil without the addition of polymer viscosity index improvers (VII's)which can shear under heat and pressure.
In the RL example you've given, neither the 5w30 nor the 10w30 oil's contain any VII's, consiquently I'd say the 5w30 is the better oil due to it's higher VI.
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For example, a fluid with a VI of 350 would be just shy of a 40 grade @ 100C (12.x cSt) ..but would only be 40Cst @ 40C. Meanwhile a fluid with a VI of 60 that would be 40cSt @ 40C would be thinned to 5.2cSt @ 100C.
The lower the number, the more the change over the temp span. The higher the number ..the less the change.
Play here. It will help you
The lower the number, the more the change over the temp span. The higher the number ..the less the change.
Play here. It will help you
Tom NJ
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Pasted from a post I made some three years ago on viscosity index.
Tom NJ
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In a nutshell, all organic liquids will thin out when heated and thicken up when cooled, but they don't all do so at the same rate. Viscosity Index is simply a scale to compare the rate of viscosity change with temperature between different fluids. A fluid that thins more upon heating and thickens more upon cooling has a lower VI than one that thins and thickens less. Or put another way, higher VI oils change their viscosity less when the temperature changes. This can be a good property for lubricants that are used in a wide temperature range and low shear rates.
The VI scale was originally established by assigning a value of "0" (zero) to the worse known base oil at the time, and "100" to the best. The theory was that all other base oils would then fall between these end points. Apparently they didn't anticipate synthetics or hydrocracked mineral oils back then.
The VI of a base oil is dictated by its chemical structure. Linear hydrocarbons have the best VI, but they also exhibit a freeze point when cold (waxes). The next best VI comes from branched hydrocarbons and the worse comes from ring compounds, such as aromatics, naphthenics, and cyclic hydrocarbons.
Group I base oils are a mix of linear and ring shaped hydrocarbons and usually have a VI around 90-100. By hydrotreating the Group I stock (reacting with hydrogen) you break a portion of the ring compounds into branched hydrocarbons, and this raises the VI and makes a Group II oil. Severely hydrotreating (called hydrocracking) the Group II opens more rings and raises the VI further (120-125), making a Group III oil. Since the VI is very sensitive to the degree of hydrotreating/cracking, it is used as a measure in defining the Groups.
PAOs are pure branched hydrocarbons and have even higher VIs, usually 125-140. Esters are hydrocarbons that also contain oxygen atoms, and can come in different shapes and sizes, so their VIs can run from 50 to 200, but most esters used in motor oils have VIs of 130 to 150. ANs are ring compounds and have lower VIs (75-105).
Viscosity Index can be important in applications that operate in a wide temperature range where the oil is expected to flow under its own weight (low shear), but there are other and better measures of performance over temperature. In motor oils, the oil is pumped (high shear) at cold start-up and the flow properties are better defined with the Cold Crank Simulator and MRV tests. Even at the high temperature end, HTHS viscosity is a better measure because it simulates the shear rates in the bearings. Hence the VI of a motor oil is not very useful in telling you how the oil will behave at start-up or at full temperature. About all its good for is giving an indication of the amount of VI Improver in the oil, but that too is deceptive.
People tend to think that less VI Improver the better, but that depends on the type of VI Improver used. Some are much more shear stable than others, and a higher quantity of a shear stable VII may be better than a lower quantity of a non-shear stable VII. In addition to permanent viscosity loss cause by breaking (shearing) the large VII molecules, they also exhibit temporary viscosity losses under high shear, and this affects the HTHS viscosity.
If only oil chemistry followed simple rules we would all be experts, but there is a lot of chemistry going on in the engine, and trying to predict or rank motor oils by comparing basic physical properties like VI, Kinematic viscosity, pour point, and flash point is pretty much a waste of time. What matters is how well they work, and since that depends on the engine design, driver, and environment, what really matters is how well they work for YOU.
Tom NJ
********************
In a nutshell, all organic liquids will thin out when heated and thicken up when cooled, but they don't all do so at the same rate. Viscosity Index is simply a scale to compare the rate of viscosity change with temperature between different fluids. A fluid that thins more upon heating and thickens more upon cooling has a lower VI than one that thins and thickens less. Or put another way, higher VI oils change their viscosity less when the temperature changes. This can be a good property for lubricants that are used in a wide temperature range and low shear rates.
The VI scale was originally established by assigning a value of "0" (zero) to the worse known base oil at the time, and "100" to the best. The theory was that all other base oils would then fall between these end points. Apparently they didn't anticipate synthetics or hydrocracked mineral oils back then.
The VI of a base oil is dictated by its chemical structure. Linear hydrocarbons have the best VI, but they also exhibit a freeze point when cold (waxes). The next best VI comes from branched hydrocarbons and the worse comes from ring compounds, such as aromatics, naphthenics, and cyclic hydrocarbons.
Group I base oils are a mix of linear and ring shaped hydrocarbons and usually have a VI around 90-100. By hydrotreating the Group I stock (reacting with hydrogen) you break a portion of the ring compounds into branched hydrocarbons, and this raises the VI and makes a Group II oil. Severely hydrotreating (called hydrocracking) the Group II opens more rings and raises the VI further (120-125), making a Group III oil. Since the VI is very sensitive to the degree of hydrotreating/cracking, it is used as a measure in defining the Groups.
PAOs are pure branched hydrocarbons and have even higher VIs, usually 125-140. Esters are hydrocarbons that also contain oxygen atoms, and can come in different shapes and sizes, so their VIs can run from 50 to 200, but most esters used in motor oils have VIs of 130 to 150. ANs are ring compounds and have lower VIs (75-105).
Viscosity Index can be important in applications that operate in a wide temperature range where the oil is expected to flow under its own weight (low shear), but there are other and better measures of performance over temperature. In motor oils, the oil is pumped (high shear) at cold start-up and the flow properties are better defined with the Cold Crank Simulator and MRV tests. Even at the high temperature end, HTHS viscosity is a better measure because it simulates the shear rates in the bearings. Hence the VI of a motor oil is not very useful in telling you how the oil will behave at start-up or at full temperature. About all its good for is giving an indication of the amount of VI Improver in the oil, but that too is deceptive.
People tend to think that less VI Improver the better, but that depends on the type of VI Improver used. Some are much more shear stable than others, and a higher quantity of a shear stable VII may be better than a lower quantity of a non-shear stable VII. In addition to permanent viscosity loss cause by breaking (shearing) the large VII molecules, they also exhibit temporary viscosity losses under high shear, and this affects the HTHS viscosity.
If only oil chemistry followed simple rules we would all be experts, but there is a lot of chemistry going on in the engine, and trying to predict or rank motor oils by comparing basic physical properties like VI, Kinematic viscosity, pour point, and flash point is pretty much a waste of time. What matters is how well they work, and since that depends on the engine design, driver, and environment, what really matters is how well they work for YOU.
It's the RATE at which a fluid changes viscosity.
Basic definition:
"Viscosity Index (V.I.) - Relationship of viscosity to temperature of a fluid. High viscosity index fluids tend to display less change in viscosity with temperature than low viscosity index fluids."
"Viscosity Index (V.I.) - Relationship of viscosity to temperature of a fluid. High viscosity index fluids tend to display less change in viscosity with temperature than low viscosity index fluids."
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