Originally Posted By: Danh
The VI (IIRC) is a product of a simple calculation of the viscosity at 100c vs 40c. While this is useful information it doesn't really tells how the oil will perform at colder temperatures.
An oil that performs a certain way between 100c and 40c will not necessarily perform the same way between 40c and -20c. So I wouldn't assume that an Mobil 1 5w30 is thinner at winter starting temps than Mobil 1 0w30.
You can easily extrapolate down well below freezing so an oils VI tells one a lot in predicting operational viscosity at non extreme cold starting temp's.
But if you really want to know how thick/thin these oils are relative to each other in terms of actual operational viscosity try them in a car with an oil pressure gauge then you'll know.
As it stands the PDS info is not detailed enough. If the HTHSV was provided to 2 decimal places instead of just one it would be helpful. The 5w30 could have a HTHSV of 3.149 rounded down to 3.1cP and the 0w30 could have a HTHSV of 2.951cP rounded up to 3.0cP. So the real difference in HTHSV could be 0.2 cP which definitely would be reflected in the 0w30 being lighter at all operating temp's despite it's marginally lower VI.
As it stands, we will just have to trust Mobil when it says their AFE 0w30 is a more fuel efficient oil than their 5w30 because for that to be true it must have a significantly lower effective HTHSV not just a 150C but also at 100C although that spec' is not provided. And for those that don't know fuel economy correlates with HTHSV.
The VI (IIRC) is a product of a simple calculation of the viscosity at 100c vs 40c. While this is useful information it doesn't really tells how the oil will perform at colder temperatures.
An oil that performs a certain way between 100c and 40c will not necessarily perform the same way between 40c and -20c. So I wouldn't assume that an Mobil 1 5w30 is thinner at winter starting temps than Mobil 1 0w30.
You can easily extrapolate down well below freezing so an oils VI tells one a lot in predicting operational viscosity at non extreme cold starting temp's.
But if you really want to know how thick/thin these oils are relative to each other in terms of actual operational viscosity try them in a car with an oil pressure gauge then you'll know.
As it stands the PDS info is not detailed enough. If the HTHSV was provided to 2 decimal places instead of just one it would be helpful. The 5w30 could have a HTHSV of 3.149 rounded down to 3.1cP and the 0w30 could have a HTHSV of 2.951cP rounded up to 3.0cP. So the real difference in HTHSV could be 0.2 cP which definitely would be reflected in the 0w30 being lighter at all operating temp's despite it's marginally lower VI.
As it stands, we will just have to trust Mobil when it says their AFE 0w30 is a more fuel efficient oil than their 5w30 because for that to be true it must have a significantly lower effective HTHSV not just a 150C but also at 100C although that spec' is not provided. And for those that don't know fuel economy correlates with HTHSV.
