Oil polarity, tendency to stay on metal over time

[partspro]

I don't know the oil that you refer to but I always believed, possibly incorrectly that PAO and ester kind of went hand in hand. Wasn't it the ester content that caused seal swelling that started the whole, 'if you go synthetic you can't switch back to Dino deal'. This was before the hydrocracked, marketing term only, synthetics that we refer to today.

 

[GMorg]

Anything that can dissolve the additive package will be fairly polar.

Today's oils should always be polar enough to keep the add pack in solution. However, the net polarity of the finished product is not as important as the polarity of individual components when you are thinking about cling during storage. The more polar solutes will collect at the metal surface as opposed to staying evenly distributed in solution.

If you have ever tried to wash off soap or shampoo in very soft water verses very hard water, you would have observed the surface effect of a solution. Soft water does not remove shampoo as well as hard water. It actually takes more water and more time to wash a detergent off when the water is very soft.

Another example is temporary dyes (like some kids use in their hair). The dye is concentrated at the substrate surface even though it is in solution.

An oil based example is the red phytochrome in tomato skin. It will stain plastic or the inside of your dishwasher but will eventually wash back off.