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topping off 5MT fluid... with what?

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Hey folks - getting things ready to swap a front axle and inevitably there will be some oil leakage. The car had it's 96000km major service 18 months ago and every fluid was replaced, so I'd rather just top it up - but no idea what to use. The service was done at the Subaru dealer so I assume they used Subaru's own gear oil.


Can I safely top it up with Red Line 75W90? Is something analogous to the subie stuff readily available?



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Well, Subaru high performance gear oil (this is not extra-s, extra-s has been superseded.) is not synthetic based, while Redlines 75w90 fluid is. I'm not a fan of mixing fluid; i'd just go back to the dealer and pick up some high performance gear oil, which is probably what they filled your gearbox with. If you have the paperwork or service records, you should be able to call and see for sure what fluid they used.


Certain dealers will just use some random GL5 bulk gear oil, certain dealers use Subaru OEM stuff, it all depends, there's really no standard or quality control in place for that.


TL;DR: I wouldn't use Redline.


Also, for future reference; I know this is kind of off-topic. I haven't heard much good using straight redline, these 5MT boxes house both syncros and the diff in the same fluid; so they're extremely picky on the type of fluid that works well with both syncros and differentials. I use straight Motul Gear 300 75w90 on my 5MT, that stuff shifts like butter in the cold. When I did my 90k fluid change, I filled the transmission with Subaru high performance gear oil, which, in my case, was notchy, caused 5th gear to grind, and felt like mud in the cold. I quickly (in 3k miles) drained that crap out, and have been running Motul Gear 300 for nearly 25k miles without issue.


Edit: Jack your car up so that the fluid rests on the opposite side of the axle that you're pulling, you should lose a very minimal amount of gear oil when you pull your old axle seal out.

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Thanks for the post! Awesome info.


Someone told me yesterday that in a 5MT car, I shouldn't lose much oil at all provided I jack up that side of the car, like you said. Apparently the instructions I had read were on a 5AT car where the oil level is a bit higher..?


I'm spending way too much money on car stuff lately so I'll try to keep as much of oil in there as I can, but thanks for the recommendation on Motul. I've supposedly got another 20k miles before I have to change fluids, but I might do it sooner if the spending slows down a bit :D

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