I could not find this elsewhere, but what is the significance of differences in viscosity index? I do know what the general meaning of VI is. My car uses 0W-20 synthetic oil and I can find the VI's for some brands of oil online and some I can't find. In another thread someone told me that Toyota 0W-20 had a VI over 200 while Mobil 1 Advanced Fuel Economy was in the 170's. All the oils for which I could find VI's online were in the 170's, including Amsoil. So, the question is how much better, really, is a 200 v. a 170?
Significance of VI Differences
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In DFW, it won't matter much if any. It's only a real issue if you live in very cold areas.
From what I've learned on here, the high the VI, the better the flow of oil and protection at start up in almost all climates.
So, I a higher VI oil (given the same weight) would flow better than a lower VI oil.
But my question is, what are the consequences of a high VI? Everything in oil, and chemistry, seems to be in balance. What I mean is, it seems that every time we improve one characteristic of an oil, you're diminishing another aspect/quality/characteristic.
So, is there a physical property that you could see decline with a higher VI? Example, and this is probably not true, but if you had two 0w20 oils, one with a VI of 150, and the other with a VI of 250, would the 250 oil be more prone to shear? Oxidation? Etc.
Thanks.
So, I a higher VI oil (given the same weight) would flow better than a lower VI oil.
But my question is, what are the consequences of a high VI? Everything in oil, and chemistry, seems to be in balance. What I mean is, it seems that every time we improve one characteristic of an oil, you're diminishing another aspect/quality/characteristic.
So, is there a physical property that you could see decline with a higher VI? Example, and this is probably not true, but if you had two 0w20 oils, one with a VI of 150, and the other with a VI of 250, would the 250 oil be more prone to shear? Oxidation? Etc.
Thanks.
The disadvantage of a high VI is shear. You can get around this by using higher quality base stocks... the the disadvantage becomes cost.
Originally Posted By: bepperb
The disadvantage of a high VI is shear. You can get around this by using higher quality base stocks... the the disadvantage becomes cost.
Not necessarily. There are plenty of shear-stable VIIs.
Mobil 1 0w40 offers a 185 VI but is quite stable under normal use.
The disadvantage of a high VI is shear. You can get around this by using higher quality base stocks... the the disadvantage becomes cost.
Not necessarily. There are plenty of shear-stable VIIs.
Mobil 1 0w40 offers a 185 VI but is quite stable under normal use.
Using Widman's VI calculator for two oils that have a KV100 of 8.5 (same as M1 ow20), but different VI's of 170 and 200 gives the following KV's at various temperatures.
VI:...170....200..% change
40C; 44.8, 39.7, -11.3
20C; 107.4, 87.8, -18.2
0C; 338.9, 246.1, -27.3
-10C; 692.1, 463.9, -32.9
You can see that at a cold start temperature of -10C, the oil with the higher VI has ~33% lower viscosity, which will make it much easier to pump, and will draw less power from the oil pump, saving fuel due to lower parasitic loss in the engine. Higher VI oils can be a significant help for fuel economy if the car sits outside and is used mostly for short trips where the oil doesn't have a chance to heat up and thin out to a normal operating viscosity.
VI:...170....200..% change
40C; 44.8, 39.7, -11.3
20C; 107.4, 87.8, -18.2
0C; 338.9, 246.1, -27.3
-10C; 692.1, 463.9, -32.9
You can see that at a cold start temperature of -10C, the oil with the higher VI has ~33% lower viscosity, which will make it much easier to pump, and will draw less power from the oil pump, saving fuel due to lower parasitic loss in the engine. Higher VI oils can be a significant help for fuel economy if the car sits outside and is used mostly for short trips where the oil doesn't have a chance to heat up and thin out to a normal operating viscosity.
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It's a could question.
A small VI difference of 10 points isn't going to be that noticeable but when you start getting into 30 plus point differences the viscosity differences between oils will become significant even at room temperature.
Using your Mobil 1 Advanced Fuel Economy 0W-20 (173 VI) example and compare it to the Mobil made Toyota 0W-20 (216 VI).
At 20C (68F) the Toyota oil is already 25% lighter than M1. At 10C (50F) that difference has climbed to 30% and to 35% at 0C (32F).
To put this into proper context the viscosity difference between a typical 20wt and 30wt oil is only 15-25%.
If you want to compare the kinematic viscosity differences of different oils at various temperatures just plug their KV40 and KV100 spec's into a viscosity graph like Widman's, see below:
http://www.widman.biz/English/Calculators/Graph.html
A small VI difference of 10 points isn't going to be that noticeable but when you start getting into 30 plus point differences the viscosity differences between oils will become significant even at room temperature.
Using your Mobil 1 Advanced Fuel Economy 0W-20 (173 VI) example and compare it to the Mobil made Toyota 0W-20 (216 VI).
At 20C (68F) the Toyota oil is already 25% lighter than M1. At 10C (50F) that difference has climbed to 30% and to 35% at 0C (32F).
To put this into proper context the viscosity difference between a typical 20wt and 30wt oil is only 15-25%.
If you want to compare the kinematic viscosity differences of different oils at various temperatures just plug their KV40 and KV100 spec's into a viscosity graph like Widman's, see below:
http://www.widman.biz/English/Calculators/Graph.html
Originally Posted By: Phishin
But my question is, what are the consequences of a high VI? Everything in oil, and chemistry, seems to be in balance. What I mean is, it seems that every time we improve one characteristic of an oil, you're diminishing another aspect/quality/characteristic.
So, is there a physical property that you could see decline with a higher VI? Example, and this is probably not true, but if you had two 0w20 oils, one with a VI of 150, and the other with a VI of 250, would the 250 oil be more prone to shear? Oxidation? Etc.
There are two way's of acheiving a high VI oil.
First start with a high quality base oil that already has a naturally high VI, possibly as high as 140 then use a high VI shear stable polymer thickener to acheive the final VI of the finished oil, possibly as high as 229 as it is with the Sustina 0W-20.
Oxidative stability and shear resistance are determined by the quality of an oil's component parts. You can have an inexpensive low VI oil that uses low VI base oils and cheap shear prone polymer thickeners that shears more than an ultra high VI oil.
For example the expensive Sustina 0W-20 uses a high quality high VI base oil (GTLE) and the latest in very high VI, shear stable polymethacrylates polymer thickeners to produce an oil shear stable as a VII free oil.
The other advantage of a high VI oil besides improved cold start performance is reduced temporary viscosity loss at high temp's. In otherwords, while a high VI oil doesn't thicken up as quickly at as the temp's drop, it also doesn't thin oil as quickly as oil temp's rise above normal, providing a greater high oil temp' safety margin compared to a low VI oil.
But my question is, what are the consequences of a high VI? Everything in oil, and chemistry, seems to be in balance. What I mean is, it seems that every time we improve one characteristic of an oil, you're diminishing another aspect/quality/characteristic.
So, is there a physical property that you could see decline with a higher VI? Example, and this is probably not true, but if you had two 0w20 oils, one with a VI of 150, and the other with a VI of 250, would the 250 oil be more prone to shear? Oxidation? Etc.
There are two way's of acheiving a high VI oil.
First start with a high quality base oil that already has a naturally high VI, possibly as high as 140 then use a high VI shear stable polymer thickener to acheive the final VI of the finished oil, possibly as high as 229 as it is with the Sustina 0W-20.
Oxidative stability and shear resistance are determined by the quality of an oil's component parts. You can have an inexpensive low VI oil that uses low VI base oils and cheap shear prone polymer thickeners that shears more than an ultra high VI oil.
For example the expensive Sustina 0W-20 uses a high quality high VI base oil (GTLE) and the latest in very high VI, shear stable polymethacrylates polymer thickeners to produce an oil shear stable as a VII free oil.
The other advantage of a high VI oil besides improved cold start performance is reduced temporary viscosity loss at high temp's. In otherwords, while a high VI oil doesn't thicken up as quickly at as the temp's drop, it also doesn't thin oil as quickly as oil temp's rise above normal, providing a greater high oil temp' safety margin compared to a low VI oil.
You hit it on the head. I was doing some reading today about the difference between "naturally" occurring VI and VI achieved with additives. One of the Amsoil sites I explored stated that only Group IV synthetics had "naturally" high VI's and that Group III's achieved their numbers with additives.
My car is an "indoor" car (garage at home, parking garage at work) and it rarely gets cold here. It does get plenty hot. I was trying to determine if I am being overly compulsive worrying over buying harder to get oil like Toyota, Sustina, or the new Mazda oil, or if I should just go with Mobil 1 Advanced Fuel Economy and call it a day.
My car is an "indoor" car (garage at home, parking garage at work) and it rarely gets cold here. It does get plenty hot. I was trying to determine if I am being overly compulsive worrying over buying harder to get oil like Toyota, Sustina, or the new Mazda oil, or if I should just go with Mobil 1 Advanced Fuel Economy and call it a day.
That high vi is only valid when the oil has been "unused". Calc a toyota 0w20 with 4k miles on it( fom our UOA vault) and I bet its about 30-40 points lower than new. Note that from A_Harmans' exercise above, that at Room temperatures the viscosity of the sample 0w20 oil is around 100cSt which is 5 times as thick as an SAE50 at engine running temps - that should make clear the benefits of high vi at even moderately livable "warm climate" starting temps. I still worry (needlessly?) about shear stability of 5 buck a qt oils.
Originally Posted By: DBMaster
I was doing some reading today about the difference between "naturally" occurring VI and VI achieved with additives. One of the Amsoil sites I explored stated that only Group IV synthetics had "naturally" high VI's and that Group III's achieved their numbers with additives.
All oils today use polymer thickeners to acheive the final VI of their finished oils.
The VI of PAO base oils are not necessarily higher than GP III oils and when it comes to GP III+ oils their VIs can even be higher than PAOs.
If I had a new Mazda I'd certainly want to try the new 225 VI, high moly, Mazda 0W-20 oil and it seems very reasonably priced at $7.95/qt or the Toyota 0W-20 if that's easier to get.
As you can see these oils are very much lighter even at room temperature than the rather "long in tooth" Mobil 1 Advanced Fuel Economy 0W-20.
I was doing some reading today about the difference between "naturally" occurring VI and VI achieved with additives. One of the Amsoil sites I explored stated that only Group IV synthetics had "naturally" high VI's and that Group III's achieved their numbers with additives.
All oils today use polymer thickeners to acheive the final VI of their finished oils.
The VI of PAO base oils are not necessarily higher than GP III oils and when it comes to GP III+ oils their VIs can even be higher than PAOs.
If I had a new Mazda I'd certainly want to try the new 225 VI, high moly, Mazda 0W-20 oil and it seems very reasonably priced at $7.95/qt or the Toyota 0W-20 if that's easier to get.
As you can see these oils are very much lighter even at room temperature than the rather "long in tooth" Mobil 1 Advanced Fuel Economy 0W-20.
Not being a student of motor oil, the only way I can rationalize the effect of differences in VI is be to look at the viscosity/temperature relationship on the widman graph.
Right or wrong, I basically look the viscosity of one oil at a particular temp and find the temp that another oil must be at to produce a similar viscosity. IE: the 8.5 kv100 / 44.8 kv40 at a particular temp has a similar viscosity of an oil with an 8.5 kv100 / 39.7 kv40 at a temp of 5 celcius degrees lower.
Right or wrong, I basically look the viscosity of one oil at a particular temp and find the temp that another oil must be at to produce a similar viscosity. IE: the 8.5 kv100 / 44.8 kv40 at a particular temp has a similar viscosity of an oil with an 8.5 kv100 / 39.7 kv40 at a temp of 5 celcius degrees lower.
Local CT Mazda dealer has in stock for $8.75/quart. They have just received inventory.
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