Transmission Fluid
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This is a discussion on Transmission Fluid within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I just changed my transmission fluid to Mobil 1 synthetic 75W90. I'm at 12,000 miles. Shifting has a much easier ...

  1. #1
    Registered User pace's Avatar
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    Transmission Fluid

    I just changed my transmission fluid to Mobil 1 synthetic 75W90. I'm at 12,000 miles. Shifting has a much easier action now. I'm curious to see if I still have the spoon-in-treacle feel on cold mornings though. What's the general consensus on Mobil-1 synthetic for the WRX tranny?

    What is everybody else using, and what are you observations. What mileage did you change at?

    -Pace

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    Registered User TristineLim's Avatar
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    I was thinking about changing mine very soon, too. You used Mobil 1, huh? hmm trying to decide between Mobil 1 and Redline. I'm at a little over 10,000 miles. Are you thinking about changing differential fluid, too?

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    Registered User pace's Avatar
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    I will probably change the diff fluid at the next oil change. Not sure what I'll use yet though - still researching!

    -Pace

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    tan
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    I've used Redline MT-90 in the past. Redline is generally well regarded for its gear oil. The MT-90 is formulated for synchro function. It shifts smooth as soft butter in the winter when the gearbox is still warm.

    Depending on the source, it may cost less than Mobil 1 or more expensive.

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    Registered User elgorey's Avatar
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    Redline MT-90 would be the perfect gear oil....except...It is only GL-4 rated and our trannies require GL-5 oil.
    Some people have used it anyway with no reported ill effects yet, but long term there could be issues.

    Redline Superlight Shockproof is also supposed to be good, especially for hard shifting
    WRB WRX STX Prepped

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    What do you guys think about changing the tranny oil to the brand royal purple? i hear it's one of the best. also if i changed my tranny fluid, is it worth it to get a flush? or should i just drain it, and not worry about it? thanks for any input.

    ---RaCinWRX

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    I did some research and this is what I found so far from what some
    rexer are using.

    Mobil 1 Motor oil, No zine and pure than other syn according to the spec I found on a motor oil site.

    Redline 75W90NS for tranny. It does not interfers with the syncron since it got less modifiers.

    Redline 75W90 for the diff. Better lube properties with modifiers.

    Hope this helps.
    What mods, dude this baby is stock
    2002 Platinum Silver 5spd sedan.

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    Registered User blarg's Avatar
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    the mechanic at the dealer told me to get all diffs and tranny done at the same time, and Redline works great...he also said wait till i hit 30K miles before I change it.

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    From what I read.

    Redline 75W90NS for tranny ( without modifier since sycrom doesn't like modifier ).

    Redline 75W90 for the diff ( with modifier for less frictions).

    Mobil 1 10w30.
    What mods, dude this baby is stock
    2002 Platinum Silver 5spd sedan.

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    Moderating on the run! Big Sky WRX's Avatar
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    I considered Redline for my tranny and diff, but read too many conflicting reports on performance in the tranny. Some were even saying a mixture of NS and regular 75W90 in the tranny was needed.

    Instead I went w/ Mobil 1 75W90 in both rear diff and tranny. That was at 10,000 miles last November. After a particuliarly long winter, I am comfortable in saying the Mobil 1 performed well. Shifting is smooth, even at below zero temps.

    We'll see how it does through the rigors of a hot summer. So far so good.

    Big Sky

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    here's a question:

    somebody told me to flush the tranny line b4 i change tranny fluids. somebody else told me that it's like changing oil and i don't need to do a flush till some 80k miles or something. who's right??

    --RaCinWRX

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    tan
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    If you have a manual transmission, no flush needed.

    Automatic, yes, since doing a simple drain & refill only changes around 80% of oil fluid.

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    thanks for the info tan

    here's another question. where's the tranny drain plug and how much oil should one buy?

    thanks again for any info ahead of time

    --RaCinWRX

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    tan
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    That I don't know (besides somewhere on the bottom of the transmission pan, and the fill plug is on the side). For oil, the manual may have it listed.

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    Get 5 quarts if you are also changing the filter.
    Put 4 1/2 quarts in and top it off slowly. Rex does not like overfill, both engine and tranny.

    I check mine when the car was cold and the tranny oil lvl was low. I went to the dealer thinking something is wrong and was told to check the tranny oil level when it is hot not cold.

    When it is cold it shows low and high when it is hot. So if you fill the tranny to high when it is cold then it will have 2 much oil in the tranny, since tran oil expands as it get hot.

    I am doing mine at 6000 with my second oil change. I will be using redline NS. As for motor oil I use Castro Syntech blend since I put in 120 miles a day I go thru oild change every quickly so Mobil 1 and fancy filter will be a waste. I check the oil at 5000 and it was still nice and clear not black.

    Btw the subie tech told me I can use synthetic tranny oil if I like just make sure it is GL5 then it is cool with the dealer.
    What mods, dude this baby is stock
    2002 Platinum Silver 5spd sedan.

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