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Author Topic: Question on Synthetic Fluids  (Read 3173 times)

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Offline Clutch

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Question on Synthetic Fluids
« on: September 29, 2014, 09:27:37 PM »
Howdy howdy.

Question for you guys that have been living in upstate through the winters with your Subarus.

Currently have two in the driveway, a 2010 forester and a 2011 Impreza.  Wanting to do some of the services that they need before it gets too cold out, but just wanted to know the thoughts on synthetic gear oil in the transmissions and differentials. 

In my previous cars I have had good luck going synthetic for all of my fluids, but Im reading on the interwebz that some of the Subaru stuff doesnt play nice with it.  I would rather not dump a bunch of $ into expensive oils if the dino stuff works just fine or is actually better. 

Appreciate any insights!

Offline Turbaru

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Re: Question on Synthetic Fluids
« Reply #1 on: September 30, 2014, 08:44:41 AM »
People have really good luck just putting Subaru LSD in the dif and Subaru Extra-S in the transmission!
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Offline deadlydave

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Re: Question on Synthetic Fluids
« Reply #2 on: September 30, 2014, 09:29:36 AM »
I've run Castrol Syntec and Edge in every car I've owned, and haven't had a complaint.  I will probably send my WRX oil to Blackstone labs for anaylsis this winter.

In both a Cusco/WRX rear LSD, the OEM 02 WRX LSD, and 02 WRX transmission in my current car, I have used LucasOil's full synth 75w90.  There's a blurb on the bottle that says it contains LSD additives.  It's only been a couple of years but the trans and rear diff have somewhere around 90,000 miles on them.  My old transmission grenaded, but I don't think the type of gear oil had anything to do with it.

Given the time, I would run the Extra-S, maybe with some Redline lightweight shift stuff and plan to run it when I do the fluids again.  Advanced 'cocktails' like Uncle Scotty's are used by guys like Vermont SportsCar to build Rally cars, but they rebuild the transmissions frequently and cycle the fluid at least once per event.  Given our climate, I'm not sure something like USC would work with constant seasonal differences.

Offline Clutch

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Re: Question on Synthetic Fluids
« Reply #3 on: September 30, 2014, 09:44:14 PM »
Thanks for the responses!

Im guessing my Impreza doesnt have the LSD, since its just the 2.5i, so then in that case would just the Extra-S and (from what I have found elsewhere) the Valvoline gear oil bet the right ticket? 

Previously I had a Mazda Protege5 that I ran Redline in the transmission, and it really seemed to help out with the shifting smoothness.  Im not one to change things just to change them, but wanted to see if a synthetic version of the gear oils might be the way to go, especially for cold weather. 

Not really looking to get into Uncle Scotty's if I can avoid it, just something about mixing and mixing when I really just want to drive my car.  Would like to avoid cycling the fluid more than the regular intervals spec'd if I can help it!

Offline wheelbuilder_25

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Re: Question on Synthetic Fluids
« Reply #4 on: September 30, 2014, 10:37:45 PM »
I've used Mobil 1 in the diffs on the Legacys I've had with good luck.  It claims to be good for LSDs, as well as open.  I think the key is regular changes with the correct fluid, more that the fluid.

I'm quite tempted to try Extra-S next change. 

Bobistheoilguy.com is a great source for oil info and debate.
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Offline Clutch

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Re: Question on Synthetic Fluids
« Reply #5 on: October 01, 2014, 06:06:59 AM »
I've used Mobil 1 in the diffs on the Legacys I've had with good luck.  It claims to be good for LSDs, as well as open.  I think the key is regular changes with the correct fluid, more that the fluid.

I'm quite tempted to try Extra-S next change. 

Bobistheoilguy.com is a great source for oil info and debate.

Thanks for the response! 

Agree that BITOG has a wealth of info, but I think probably too much at times.  I know that I could get a good oil recommendation, but didnt know if it would be Subaru specific.  I figured everyone here on this board would have pretty similar weather conditions to contend with, and a little bit better "real world" experience. 

Offline Clutch

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Re: Question on Synthetic Fluids
« Reply #6 on: October 20, 2014, 06:55:08 PM »
So after reading, and reading, and reading some more.....

I think Im going to just go with Extra-S in the transmission for my Impreza, and Im tempted to go with some Amsoil Severe Gear 75w-90 in the rear diff.  Same with the Forester, except that will get the Amsoil in the front and rear diff (auto tranny).  Is there a service interval for the automatic transmission fluid when not performing a flush?

Sounds like the transmissions are a little bit touchy about what they like, so might as well stick with a known good fluid there.  But I wouldnt mind trying to save a little bit of friction in the diffs where it doesnt seem quite as crucial. 

Offline madlife

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Re: Question on Synthetic Fluids
« Reply #7 on: October 21, 2014, 07:56:08 AM »
I think Im going to just go with Extra-S in the transmission for my Impreza, and Im tempted to go with some Amsoil Severe Gear 75w-90 in the rear diff.  Same with the Forester, except that will get the Amsoil in the front and rear diff (auto tranny).  Is there a service interval for the automatic transmission fluid when not performing a flush?

I swapped to Extra-S in my last WRX and one of the biggest improvements I noticed was how much better it shifted int he winter when i first started the car up.   It didnt feel like I was trying to swim in mud

Offline wheelbuilder_25

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Re: Question on Synthetic Fluids
« Reply #8 on: November 05, 2014, 09:27:54 AM »
So after reading, and reading, and reading some more.....

I think Im going to just go with Extra-S in the transmission for my Impreza, and Im tempted to go with some Amsoil Severe Gear 75w-90 in the rear diff.  Same with the Forester, except that will get the Amsoil in the front and rear diff (auto tranny).  Is there a service interval for the automatic transmission fluid when not performing a flush?

Sounds like the transmissions are a little bit touchy about what they like, so might as well stick with a known good fluid there.  But I wouldnt mind trying to save a little bit of friction in the diffs where it doesnt seem quite as crucial.

I believe the owner's manual suggests ATF drain and fill every 30k. (severe is 15k)

Somewhere in my travels I've seen that in either 2007 or 2008 Subaru changed friction materials in the 4EAT and it requires Subaru's ATF HP fluid, NOT Dexron.  (except for top off)  That's what I've used in the 2009 (per the manual), and it shifts as well as ever.
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Offline Clutch

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Re: Question on Synthetic Fluids
« Reply #9 on: November 07, 2014, 12:47:50 PM »
Got the Extra-S (or "Subaru High Performance Gear Oil" as its apparently now known) in and the shifts are definitely smoother.  Perhaps its placebo effect right now, but Ill keep up with it over the next few weeks to see if it stays nice and smooth.

Good to know on the ATF drain and fill....  I just wasnt sure if the drain/fill was enough, or if it needed a flush.
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