Is PAO content harmful to engine gaskets?

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United States
This may sound like an uneducated question, but is there any evidence that PAO based oils (such as M1 EP 0W-20 that supposedly has 60-70% PAO) will cause oil leaks because they do not swell seals as good as something like a Group III(or III+) synthetic or ester based oil? Such as will it over time if I ran an engine on M1 EP 0W20 would have likely more oil seepage than something like Castrol EDGE 0W20 black bottle (mineral oil based/largely group III)? I am asking because I read somewhere else (can't find the webpage anymore) that it mentioned that PAOs shrink/harden seals.
 

OVERKILL

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PAO-based lubricants are dosed with components that counteract the seal shrinking effects; to effectively neutralize them. So no, it isn't something to be worried about.
 
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Originally Posted by OVERKILL
PAO-based lubricants are dosed with components that counteract the seal shrinking effects; to effectively neutralize them. So no, it isn't something to be worried about.
This. Mobil 1 also contains varying percentages of Group V AN, which is quite good for seals...
 
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South Carolina
PAO by itself is known to shrink seals so oils that contain a lot of PAO also contain 5-15% ester or naphthalene to counter that effect. You shouldn't have any concerns over seal shrinkage and leaks with M1 0w-20 or any modern synthetic.
 
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4,030
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WA
Originally Posted by OilUzer
Do other base oils require a perfect/exact neutralizing mixture to be seal friendly?
All finished lubes contain seal conditioners of some kind to mitigate shrinkage/cracking/deformation. The more severely an oil is treated (purity & saturation) the lower it's solubility and lubricity is. This also applies to GTL's and PAO's. Low solubility not only makes it difficult to dissolve some additives, but it also compromises some parameters such as seal compatibility. So formulators compensate by including solubility and lubricity improvers in the finished product. Another example of the careful balancing of all things by the formulator.
 
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Curious if there are any documented long term seal tests with different oils e.g. syn vs. dino, etc. or the impact of different oils on seals after 100K miles. What exact test does API impose or what are the seal test requirements in API? I remember SonOfJoe saying that API SL is more seal friendly or not as harsh ... Can't recall the exact reason but must be due to formulation changes and limitation and/or excess of some chemicals in SL vs. SN for example. btw, Castrol still sells Edge A3/B4 0W30 API SL for $10 per quart! shocked2 I think it's the old or similar to old GC.
 
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17,241
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Upper Midwest
Originally Posted by OilUzer
Curious if there are any documented long term seal tests with different oils e.g. syn vs. dino, etc. or the impact of different oils on seals after 100K miles. What exact test does API impose or what are the seal test requirements in API? I remember SonOfJoe saying that API SL is more seal friendly or not as harsh ... Can't recall the exact reason but must be due to formulation changes and limitation and/or excess of some chemicals in SL vs. SN for example.
This is for SN oil, lifted from the Afton Specification Handbook. As for particulars of the tests you'd have to consult the specific ASTM procedure. [Linked Image]
 
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4,030
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WA
Good find.i was just going to mention that there must be some ASTMs out there that rubber mfgs have to test to.
 

SR5

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Originally Posted by OilUzer
btw, Castrol still sells Edge A3/B4 0W30 API SL for $10 per quart! I think it's the old or similar to old GC.
That Edge 5W30 A3/B4 is a great oil if you can get it at a good price. It's a Group III synthetic that carries the OEMs MB229.5 and BMW LL-01, so you know it's a good oil with those spec's. High HTHS (> 3.5 cP) and low Noack (< 10%). It passes all the API SN quality tests too, but it's only rated SL due to the fact it carries about 1000 ppm ZDDP and so it's over the Phos limit for a 30 grade. M1 and Edge 0W40 carry the same zinc / Phos levels, but being a 40 grade, they have higher chemical limits under API and so can be labeled SN. I believe GC was Group IV (PAO) based.
 
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