Originally Posted By: chubbs1
I thought PAO was poor for the seals. I Think you have it backwards, esters are good for seals. I know you know a lot more than me so I am interested if I'm wrong or the source in Lubes and Greases Magazine (Oct. 2010 Issue pg.45) Is this wrong?
Lubes 'N Greases Magazine
Esters cause seals to swell and soften, while PAOs cause seals to shrink and harden. Generally, a
little swelling and softening is better than shrinking and hardening, but there is such a thing as too much.
The degree to which esters affect seals depends on the chemical structure of the ester. Low molecular weight esters are more aggressive to seals, as are those with more ester linkages (COOR) or an aromatic ring. Such esters in high dosages can weaken and degrade seals over time to the point where they may leak or fail. This is why high ester content formulations are usually balanced with PAOs to lessen the seal effect.
Likewise, formulations with too high a PAO content could cause seal leakage or failure over time, which is why they are balanced with esters or seal swell additives.
There are a number of other factors that also influence the effects of esters and PAOs on seals, such as seal chemistry, seal variability, temperature, and load.
In reality, none of this is relevent in well formulated motor oils since seal effects are measured and controlled in the formulating process.
Personally, I would avoid any oil that claims to be based entirely on esters or PAOs unless I knew the complete formulation and how the formulator dealt with seal balance.
Tom NJ
