I was checking over my parent's 2007 Impreza Wagon with a 4EAT and it looks like transmission fluid and diff fluid should be changed. For the differential I only checked the diff fluid dipstick that is in the engine bay.

Any advice on going about changing the fluids, in terms of particular brands of fluids to use, and anything to look out for. It seems pretty straight forward. I know there are some filters for the transmission, do those have to be replace also? I see a filter on the side of the 4EAT (looks like an oil filter), but i read somewhere there is another internal filter, is this true?


I was going to use the Amsoil ATF for the transmission. What about the diffs?
I believe the car has 3 diffs, so should/can i change the fluid in all of them?

Two diffs = 2 L of 75-90 gear oil
I changed the trany fluid twice in one day because only about 6L of fluid comes out so I bought 12 L of fluid, as for the trany filters you don't change the inside filter just the outside...

How many miles does the car have? Seems premature to change.

Then again, don't follow my example and wait until 90k miles.....

If you're willing to spend the money on fluids like Amsoil, their Severe Gear 75W-90 is a good, balanced gear oil to use. Renewable Lube and Schaeffer also make outstanding gear oils. If you decide to use a 'conventional' (not 'synthetic,' aka less expensive) gear oil, use an 80W-90 instead of a 75W-90. Schaeffer and RenewableLube also make outstanding ATFs for the Subaru.

If you want an 80W-90 gear oil, Schaeffer's #267 is just about the toughest their is.

Just change the filter on the side of the transmission. Don't try opening it up or anything.

there is a little over 25k miles on the car. it is early according to the recommended change intervals, but for some reason i just feel it needs to be changed. weather conditions up where they live are kind of severe, and during the winter i know the AWD was really pushed a lot. plus i know they let my little brother drive the car and he is kind of a jackass sometimes...ok who am i kidding, when i used to borrow it from them and there was a foot of snow on the road in the winter i pretended i was Petter Solberg, haha.

thanks for the recommendations guys.

ok who am i kidding, when i used to borrow it from them and there was a foot of snow on the road in the winter i pretended i was Petter Solberg, haha.

Change that fluid YESTERDAY! :-)

Bill in SD

there is a little over 25k miles on the car.

Anytime after 5-10,000 miles on the car is the best time to change the diff fluids. The diffs are worn-in by 5-10k and clean fluid at that point will do wonders for their life. After that, you probably won't need to change them very often. ATF does not follow this pattern.

damn, why doesn't the owner's manual mention that? it makes sense though that there is some "break-in" for the diffs, so after the first fluid change maybe then the recommended change interval is ok.

oh and is that Amsoil Severe Gear the same stuff people use for manual trannys?

I've heard that they do use it in the manual transmissions. I do not, but I've heard folks say they do.

oh and is that Amsoil Severe Gear the same stuff people use for manual trannys?

I use the Amsoil Severe Gear 75W-90 in my STi 6MT. I haven't had any problems with it. It seems to be just as good or better than the original fluid, although I don't do any powershifting or any of that craziness, so who can say for sure...

is the Severe Gear 75W-90 good to use in the WRX 5MT also?

Anytime after 5-10,000 miles on the car is the best time to change the diff fluids. The diffs are worn-in by 5-10k and clean fluid at that point will do wonders for their life. After that, you probably won't need to change them very often. ATF does not follow this pattern.

Good advise.

Where I work, we change out the tranny and rear diff fluids on new semi's after about a weeks use or 2500 miles.

If you are trying to stay with Subaru Severe Service recs. both differentials and Auto trans fluid should be replaced every 15000 miles.

yup fluid has been ordered and will be changed immediately. thanks guys.

Anytime after 5-10,000 miles on the car is the best time to change the diff fluids. The diffs are worn-in by 5-10k and clean fluid at that point will do wonders for their life. After that, you probably won't need to change them very often. ATF does not follow this pattern.

Yeah I've seen some trucks run for some time after a diff fluid change and have the stuff come out golden, so I'd say just change it at around 10k miles and wait till maybe 60k to do it again...I do wonder about an MT though.

well i changed the fluids today. everything was pretty straight forward except i had to order that damn Torx T-70 bit for the front diff, and only 4 litres of fluid came out of the AT. the manual says capacity is something on the order of 9+ litres.

anyway, so i put 4 litres of fluid back in the tranny, but now it reads over full. actually it's kind of hard to read the ATF dipstick, the fluid doesn't seem to stick to the metal very uniformly. should i just drive it around a bit and then check again, or empty out some ATF (that will be fun i am sure, haha)?

The best way to check ATF is to drive it around for a few miles first, then park it on a perfectly level surface and leave it idling while you check it. If you overfilled it, go ahead and drain some or all out and start over, because excessive ATF can cause problems.

Oh and ATs never drain out completely; the torque converter holds most of it, hence the reason many shops sell a flush which gets about 95% of the old fluid out.

Sorry, I also completely forgot to tell you about the T-70 torx. Those are hard to find at times.

double post...

ah ok. i don't usually change the fluids for ATs. seems a lot simpler with Manual trannys. :)
so is the recommended service interval based on a full flush of the transmission or just simply draining whatever comes out via the drain? what is the best thing to do if i don't have one of those flush machines?

i just figured if i put in the same amount i took out it should be ok. i'll check again tomorrow.


and yeah, i knew about the T-70 being hard to find but i thought some place in town would have it. nope! T-55 was the biggest i found.

Recommended replacement interval is based on drain and re-fill.

Putting in the same amount you took out is the smart thing to do, assuming a bobo mechanic didn't overfill it in the past.

For my year, to check the level you run the gear selector through all of it's positions, with a few seconds in each one, then leave the car running in P and check the level while idling.

If I understand it correctly, the fluid will read high if the car is off. I went through the same thought process the first time I changed my ATF. "Why is it high? I put the same amount in!"

Also, that external filter does not need to be changed every time you change the fluid. I think it's a 150k part.

To back up nardvark, I think you run through all the gear selections since the transmission is one big hydraulic pump - so some parts of the transmission don't get fluid pumped back in until you hit all the gears, at least drive, since the tourque converter holds a good amount as well.

After fluid is in all the right places, you will be able to measure the amount in the reservoir correctly.

I changed my spin off filter at 120k. Made some shifts smoother.

Since you don't get all the fluid out every dump/fill, you should repeat it at least 1 or 2 more times to get all the old fluid out. 4 ltr out every time, with a 9+ capacity = repeat until fluid is almost totally replaced.

the external filter is a 15k or 30k change interval.. not 150k or 120k

Perhaps this has changed since my model year, so I apologize if the information is wrong for the poster's year, but my '02 owner's manual states "ATF filter is maintenance free part. ATF filter needs replacement, when it is physically damaged or ATF leaked."

Nardvark's information about the filter is correct and matches Subaru's specification.