Best fluids options for rear diff and front transaxle on '19 WRX

[Fahrenheit85]

My '19 WRX is getting close to 20k on it, I spent an embarrassing amount of time researching engine oil on bob the oil guy before settling on one (Pennzoil Plat 5/30 incase you were wondering). I'm not so sure I have the mental fortitude to go down that road again and i'm hoping someone here can just tell me what to use so my wife doesn't make me sleep on the sofa because I mumble UOA results in my sleep. Was thinking i'd do 20k intervals for it though that might be often, not super sure on that. Any input would be delightful, thanks for reading.

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[Big-E]

Use Motul Motyl-Gear 75W-80 for the transmission/front differential and Motul Gear-300 for the rear differential.

[Fahrenheit85]

Originally Posted by Big-E

Use Motul Motyl-Gear 75W-80 for the transmission/front differential and Motul Gear-300 for the rear differential.

Any reason for 75W-80 over 75W-90? Also what weight for the rear?

[bluesubie]

Interesting that you ended up choosing a GF5 oil after research on BITOG. The 20 weight uoa’s usually scare most people away. Check out the Rotella MV 5W-30 discussions there.

[Fahrenheit85]

Originally Posted by bluesubie

Interesting that you ended up choosing a GF5 oil after research on BITOG. The 20 weight uoa’s usually scare most people away. Check out the Rotella MV 5W-30 discussions there.

Please god don't do this to me, I spent so much time on engine oil, I was under the impression the Penn Plat would be the best to help with the carbon buildup in direct injected engines, at least for oils I could pick up at Wally World. I run 5/30 in my car

[bluesubie]

Originally Posted by Fahrenheit85

Please god don't do this to me, I spent so much time on engine oil, I was under the impression the Penn Plat would be the best to help with the carbon buildup in direct injected engines, at least for oils I could pick up at Wally World. I run 5/30 in my car

Yes, good oil and any API SN+ dexos 1 Gen 2 oil will help mitigate carbon build up, but anything with an HTHS of less than 3.5 typically shears to a 20 grade. Look for the 2015+ WRX thread here on nasioc. But as far as UOA wear goes, stock WRX’s still show low numbers with high fuel contamination and low viscosity. Probably depends on your application.

Here’s a Rotella MV uoa from an FXT.


https://www.bobistheoilguy.com/forum...-km-4500-miles

[Big-E]

Originally Posted by Fahrenheit85

Any reason for 75W-80 over 75W-90? Also what weight for the rear?

If you have an automatic, based on my delving into the FSM's, the front differential requires 75w-80. With regard to the new 2015+ WRX manual transmission, it also should take the 75w-80. I went out of my way to figure this out for a friend that has a 2015 WRX and this is what I used. After the change of fluid, I noted no difference in shifting or related, the shifting was smooth.

With regard to the rear differential, I did not specify the weight, only the brand. The Motul Gear-300 is a 75w-90.

Depending on ambient temperature or use, you can use a 90-weight in the rear differential.

With regard to engine oil, whether it was for my 2006 WRX, our 2015 FXT or our 2016 STI, I use Schaeffer 9000 synthetic 5w-40.

[Jersey Man10]

Pretty sure the intervals are 30k no?

[raisingAnarchy]

Just get an oil sample from a reputable place like DysonAnalysis. You're sitting there doing all this research and what you'll find is you still probably don't know squat (I've been there myself, trust me).

It'll cost you the same doing high $ analysis (Dyson) as it would just switching to Motul and using arbitrary OCIs with no expert opinion anyway.