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Blending oils with different VI's, is it just arithmetic mean? #5433404 05/19/20 02:37 PM
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TravlinTech Offline OP
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I just have a basic question.

The oil in both cases is AW ISO 46 hydraulic oil, there is 275 gallons total.

If you combine the following.

220 gallons of ISO 46 where the VI is 156.25. Then take 55 gallons of ISO 46 where the VI is 100.

With the above fluids blended together for a total of 275 gallons, would you agree that the combined VI is 145, approximately?

Thank you for your thoughts on this.

Re: Blending oils with different VI's, is it just arithmetic mean? [Re: TravlinTech] #5433447 05/19/20 03:38 PM
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ABN_CBT_ENGR Offline
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No, you will get a Frankenstein mixture with properties all over the place.

You mix refined base stocks (not finished oils) on C count to get a rough finished VI then add additives to finalize it for a given VI at a desired temp range.

Pouring 2 finished oils in a blender is going to get you a soup with undefined qualities and some additives could attack each other.

Even then it wouldn't be stable throughout a temperature range

Re: Blending oils with different VI's, is it just arithmetic mean? [Re: TravlinTech] #5433448 05/19/20 03:38 PM
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JimPghPA Offline
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One thing that I know you should keep in mind when you blend oils is that the physical properties of the individual molecules will not change much.

If you blend an oil that has a phase transfer of turning into a wax at a certain temperature (lets say 20 F for example) with an oil that has a phase transfer of turning into a wax at a lower temperature (lets say - 50 F for example) the molecules of the oil that change into a wax at the higher temperature will still change into the wax at or very close to the same temperature. So as an example in this mix, from 20 F to -49 F you will have a slush of wax molecules and liquid molecules.

In other words the cold performance of the individual molecules does not change, though you MAY end up with a slush that is still pumpable compared to a wax that will not pump if the oil that changed state at the higher temperature were the only oil used.

Also only pure oils change phase at exactly one temperature. Most oils are not a pure oil of only carbon molecules of only the same length, and each individual molecule chain length has a specific temperature that it changes phase at.

And also when you mix oils of different viscosity (AT TEMPERATURES THAT DO NOT CAUSE A PHASE CHANGE TO ANY OF THE MOLECULES OF THE INDIVIDUAL OIL MOLECULES OF THE MIX ) you end up with an oil close to the average of the two weighed with respect to the concentration of each, but not exactly that number. There are formulas for figuring out what that number is, but I do not know them.

And as ABN pointed out, there is some concern in some cases about the additives interacting.

Last edited by JimPghPA; 05/19/20 03:58 PM.

Boy will I be happy when ALL vehicles on public roads are autonomous.


JimPghPa

Re: Blending oils with different VI's, is it just arithmetic mean? [Re: TravlinTech] #5434685 05/20/20 11:08 PM
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MolaKule Offline
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Originally Posted by TravlinTech
I

220 gallons of ISO 46 where the VI is 156.25. Then take 55 gallons of ISO 46 where the VI is 100.

With the above fluids blended together for a total of 275 gallons, would you agree that the combined VI is 145, approximately?


No because there are so many variables here. For one the mineral oil HF will have specific PourPoint depressents in it which is a form of VII.

Then you have to take into consideration the VI of each base oil and the synthetic oil will have a different VI than the mineral oil.

Have it tested by a reputable lab and find out.


"As engineers [and scientists] we are wired to solve problems and to create new things, to challenge the status quo and push the limits..." Ken Hurt, Embry-Riddle University, Class of '97.
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