2004 3.0 H6 DIY Transmission service.

[SubiDuby]

It seems like a fairly easy job but I'm still trying to understand the specifics so I can feel confident performing the job.

I see videos on YT of people just draining the transmission, putting new fluid of equal amount to what was drained, running through the gears a few times and then you're good. However, that doesn't seem right.

Here is a how-to I found that seems more legit: https://www.subaruoutback.org/threads/changing-automatic-transmission-fluid-is-easy.5843/

What I'm struggling with is understanding the draining of the fluid multiple times after driving multiple times to fully get all the fluid out of the system. How does that work exactly? is it truly necessary or can I just do the quick drain and fill?

I'm working on my girl's 2004 outback 3.0 H6 with 230k miles and I need to do this right.

Anybody know the exact filter, the exact type of ATF fluid and the exact amount to use for this model?

I'm also planning on throwing in a bottle of the Lucas Stops Slip (24oz) in place of the some the fluid.

Really trying to simplify this process for a very detail-oriented mind that tends to overcomplicate things.

Thank you for any help!

[heartless]

the reason for the multiple drain/fill intervals is because roughly 2/3rds of the fluid is trapped in the torque converter. the only way to evacuate fluid from the torque converter is to run it. draining the pan alone will only drain about 1/3rd of the total amount of fluid in the system.

most do 3 drain/fills with some driving time between each to fully circulate the fluid.

I would not use the entire bottle of Lucas in one go.. i would only use about 1/3 of the bottle for each drain/fill cycle.

Owners manual should give you a recommended fluid type, possibly filter too.

you can download a service manual for your car from here for more info: http://jdmfsm.info/Auto/Japan/Subaru/

[1 Lucky Texan]

I saw someone do the math once, 3 drain/fills gets you over 80% new fluid.

There are a coupla methods I think to do a full fluid replacement but they are less DIY 'friendly' than just using the drain plug.

I use Valvoline MaxLife in our 03.

Edited November 15, 2019 by 1 Lucky Texan

[Numbchux]

Yep, without disassembling your transmission, you cannot get all the fluid out. So you get 1/3-1/2 out, run it to mix the old with the new, and repeat. You can just do a single drain-and-fill, but do it often, or if it's long overdue, do a few consecutively. This is why there are flushing machines that hook up to the cooler lines to completely replace the fluid with fresh as the old is pumped out of the trans (expensive, overkill, and frequently can require replacing those cooler hoses after they've been messed with).

It calls for Dexron II. Which was replaced with Dexron II. Dex/Merc covers that, and is by far the most common ATF you can buy. I buy 2.5 gallon jugs of it at the local farm/fleet store for about $1.50/qt, and do a partial change every 10k to keep it fresh (my philosophy is the best fluid is new fluid). Subaru HP is a synthetic fluid designed for the ~'08+ cars that is backwards compatible, that's probably the best fluid you can buy. There are probably dozens of options, and thousands of opinions on what's best.

I did a bunch of searching about the filter, the OE one is surprisingly expensive ($40? IIRC), and there are a bunch of aftermarket part numbers that will fit for cheap (<$10). Most appeared to be an engine oil filter, with a very different micron rating than OE (forgive me, it's probably been 5 years since I did the homework). Ultimately, I decided that it was OE only, which is not like me. FYI it's a spin-on filter, mounted behind the bumper/fog light on the LH side. You have to undo a few of the clips, and peel back the front edge of the fender liner from the bumper to get to it.

[GeneralDisorder]

You can disconnect the cooler supply hose, run the engine till the pan is empty (about a gallon), then fill it up and run it again till you get to clean fluid at the cooler supply and fill it a third time. It's a bit of a process but it can be done. We generally just recommend two services a few hundred miles apart and that typically does the job. But I have done it the complete exchange method when changing fluid types on race transmissions and such.

We use the Amsoil EA15K12 filters for the transmission. They are about $15 and are rated for this application plus they are a much higher quality filter than stock. We have been using them for years and not a single issue to report. 

We also use synthetic Amsoil OE ATF. It is compatible to both older Subarus as well as ATF-HP. much easier to just stock the one type and it far exceeds both of the required specifications. 

GD

Edited November 15, 2019 by GeneralDisorder

[CNY_Dave]

I cannot recc enough using a simple suction device from above.

I bought a liquivac one, it works well, is easy to drain, and I had a small problem with it and the company sent me a new part pronto!

https://www.tractorsupply.com/tsc/product/liquivac-oil-change-system-large-engine-project-model

 

[GeneralDisorder]

But the Subaru pans have a drain plug. So I'm not seeing how that's really all that useful. And if you unhook the cooler supply the trans will pump it out for you if you are doing a full exchange. 

GD

[1997reduxe]

The question you need to ask is how many miles ago did you have the trans serviced? It sounds like pretty many. It’s a matter of perspective 230k is a gift already, change it a few times and keep doing it, it will probably go well over 300k if you haven’t had problems yet. Personally I followed a lot of the theories about trans fluids, I have a 95 manual but I tried Mobil 1 synthetic, bad idea. I went back to old fashioned valvoline before I totally ruined it. 

Id use the fluid that was recommended for the car in the manual it came with. No additives. Sube may make reverse compatible fluids, but then I don’t even think they’ll work on my 95 anymore.

they don’t even like to see me pull in their lot for parts. Haha.

[el_freddo]

10 hours ago, GeneralDisorder said:

 if you unhook the cooler supply the trans will pump it out for you if you are doing a full exchange. 

@GeneralDisorder - is there a particular process in doing this? 

I have three questions about doing this: 

- do you run the engine in park, neutral or drive to pump out all the fluid? 

- when the fluid is pumping out, do you have the other tube sucking fresh fluid or leave it open until the flow reduces from the outlet hose? 

- replace the filter at which point in the procedure? 

Cheers 

Bennie

[GeneralDisorder]

Trans in park. Run it till the flow indicates the pan is empty. Change the filter after. 

GD

[idosubaru]

Don’t use additive. Change the fluid.  Choose better ATF fluids or change methods, rather than additives for improvements. 

Ive done all three - multiple drain and fills, pull hose and dump fluid , and pull both hoses and submerge supply side in bucket of new fluid. It’s been awhile since I’ve done that last one, if it doesn’t suck the fluid just stop when the dumping line vacated and top off.

take your pick.  They all result in substantial amounts of fluid changed.
 

 If you’re so concerned that additives sound appealing then ditch that idea and go through the extra work of pulling hoses and dumping higher percentages of old fluid.  And buy better ATF like Subaru’s new HP, amsoil, or some people like red line.  That’ll be worth your time and money, the Lucas additive won’t be worth anything except placating some false sense of value and validating their marketing budgets.  

additives rarely have value for Subaru’s, there are a few exceptions, but this isn’t one of them.  Those transmissions are robust, they just need good, new fluid.

Edited November 16, 2019 by idosubaru

[SubiDuby]

I really appreciate the insight from everyone. Thank you all!

I don't know when this car last had its tranny serviced, we acquired it somewhere around 217k, I was told its got really dirty trans fluid by a mechanic shop.

I'm getting closer to doing this job. Probably going to just keep it simple for now and do three drains/fills over a few week's time. Her commute isn't far so I'll let her get 100 miles in between each session. A few more questions I have are:

- If I'm going to do it 3 times should I just wait until after the 3rd time to replace the filter?

- Shop said her trans cooler lines are leaking and I should replace them. Are those the same hoses you pull for the substantial drain?

- I've always used Castrol for my oil changes on my Chevy truck. Would a Castrol high mileage trans fluid be a good option? Those others mentioned (subaru HP,  amsoil, redline) seem more expensive and trying to keep high costs down. Is "High Mileage" Trans fluid worth it or just a marketing ploy to get people to pay more for fluid? 

- Is there a best bang for your buck trans fluid to recommend? I've heard a few people recommend that Valvoline max life but still not sure which to spend the money on.

- Finding the total amount of trans fluid in the service manual didn't seem to give a straight answer. If you're draining approximately 4 quarts each time x 3, that's about 3 gallon jugs of trans fluid, does that sound about right?

Thanks again!

[CNY_Dave]

On 11/15/2019 at 12:28 PM, GeneralDisorder said:

But the Subaru pans have a drain plug. So I'm not seeing how that's really all that useful. And if you unhook the cooler supply the trans will pump it out for you if you are doing a full exchange. 

GD

It is much easier and much neater and so much more likely to be done regularly.

Also anytime fiddling with a drain pan plug or a hose there is a non-zero probability of a problem.

So for me, $50 bucks to make a task much easier and much cleaner is an easy call.

[idosubaru]

On 11/19/2019 at 3:28 PM, SubiDuby said:

- Is there a best bang for your buck trans fluid to recommend? I've heard a few people recommend that Valvoline max life but still not sure which to spend the money on.

"high mileage" is pointless.  get any cheap on sale compatible ATF and it'll work fine.