synthetics and seals

[JonS]

I don't fully understand POA, Esters ect. But as far as seal compatibility, which is desired, and which brands have them. I guess i just assumed a group III would tend to leak less than a true synthetic.
Out of Amsoil, Mobil 1, and group III's, which are better for an older(1995)vehicle?

 

[sub_zero]

The only one you really have to worry about are the Esters. An Ester is basically a material that is the product of an Acid/Alcohol reaction, a class of materials. As such there are many different individual types of Ester materials.

Some esters will cause seal materials like Neoprene and Buna-N to lose there elasticity or become brittle. In these applications a less reactive material usually a fluorocarbon such as Viton is used.

As for the automotive lubricants, I don't think many are formulated to incompatible with standard seal materials, like I say there are many different esters.

 

[Al]

There is honestly no issue with seal leaking anymore unless you go back to the 70's vintage vehicles. PAO's shrink seals so therefore PAO bases like Mobil 1 use Estors which swells seals. So the net effect is to neutralize seal swelling/shrinkage. I believe Redline whi8ch is mostly an Ester uses an agent (not a PAO) to neutralize any seal problems. A group III needs nothing for seal deterioration (as far as I know-I could be wrong)

As far as your oil choices, Group III is not as good base as a PAO. But as far as seal deterioration in that year-its an non issue. Some folks have stated that you do tend to get more oil seeepage in a gasket which is already on the verge of leaking (with a PAO)