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Driving a 2009 wrx, mileage at 89k.

I've always used full synthetic motor oil, mostly using Mobil 1 full synthetic on my wrx. After looking throughout the internet, I've seen a lot of subie drivers using Rotella T6 synthetic, so I decided to try it out.

My usual interval for a change is 5k. My car has never burned oil.

After a discussion with a coworker, he has told me if I go full synthetic, that I should never stop using it because if I don't continue to use it then my seals can start weeping.

Question: is it okay to go from "full synthetic" to just "synthetic"? Ive read that synthetic T6 is not fully synthetic, will this matter for me?

Also for an oil filter I've gone with an STP extended Life filter, the employee at auto zone said it will allow for 4-6k miles between changes. Any insight on oil filters? Or any recommendations?

I know these questions have probably been asked before, but i don't have time to search the forums to find an answer to my specific question on full synthetic vs synthetic. Thanks in advance

Also, this is my first post on the forums.

Jeff
 

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Tell your coworker to update his information. It's 30 years old and backwards. The seal issue has not been an issue since the late 80's. Mineral-based oils react with rubber, neoprene, etc. causing the seals to swell. This caused seal wear. Synthetic oils did not do this. Therefore when an engine was switched to synthetic oil after running mineral-based oil the seals would shrink back to normal. The wear caused to the seals when they were swelled would allow the synthetic oil to seep past them. This was rectified by putting an additive in synthetic oil that swells the seals in a way similar to mineral-based oils.

I use the OE Subaru blue filters.
 

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Discussion Starter #3
Awesome thanks! Haha yup I'll let him know, he is 10+ years older than me, so his info would be from the 80s. Appreciate it thanks! Doing the oil change tomorrow.
 

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Yeah, I don't think that's true. I've occasionally alternated back and forth on a Subaru as old as 2003 and it didn't seem to make any difference.

Side note, I do believe T6 is full synthetic. Where did you read otherwise? T5 and other Rotella variants can be syn blends, but my understanding is T6 is a true synthetic. Whether it is or isn't, tons and tons of people have had good results from it. I plan to make the switch once my warranty expires (not worth the likely battle if I ever need warranty work).
 

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T6 is full synthetic. I personally like it and have used it in many other cars other this Subaru. Keep in mind that some say that the formulation has changed so it may not have as high of zinc as they once said it did.
 
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