To flush or not to flush?

[x__CRASH__x]

I couldn't find a discussion on the subject. My '05 has 125k on it. I bought it with 115k. I have no idea if the transmission has ever been serviced. Of diffs, or timing belt... but I'll get all that... anyway...

 

Should I get the transmission fluid flushed? I've heard that can "knock things loose" and cause more problems than it solves. And that draining and putting in 4 qt's at a time over the course of a month will be fine... but will it? Old fluid will still be in there.

 

Also, what modern ATM fluid is recommended best? The stuff my manual suggests isn't available.

[Chris GTO TT]

Do a pan drain and fill first drive that around for a week or so. Then follow the instructions in the DIY section here for a fluid exchange by disconnecting the coolant line.

 

As for the fluid Amsoil or OEM Subaru ATF-HP.

[x__CRASH__x]

Thanks. Picked up some ATF-HP today. I don't see a DIY section? Can you link it?

[racerj782011]

Thanks. Picked up some ATF-HP today. I don't see a DIY section? Can you link it?

 

http://legacygt.com/forums/forumdisplay.php/walkthroughs-basic-operation-maintenance-36.html

[Leviman]

I've always heard that the reason not to change is that the worn friction material is suspended in the fluid, acting as a friction modifier to keep the old clutches working. Under that theory, it would not be recommended to change fluid.

[x__CRASH__x]

http://legacygt.com/forums/forumdisplay.php/walkthroughs-basic-operation-maintenance-36.html

 

Holy smokes... there is a whole DIY section! I never saw that!

 

Thanks!

[x__CRASH__x]

I've always heard that the reason not to change is that the worn friction material is suspended in the fluid, acting as a friction modifier to keep the old clutches working. Under that theory, it would not be recommended to change fluid.

 

I'm no mechanic, but I think this line of thinking is just wrong. There was a comment in the Walk-thru forum that if your car has over 100k you shouldn't do the flush, but doing it at 30k and 60k is fine. Unfortunately I have no idea what maintenance has been performed on my '05. I have a couple records, but nothing about tranny service. So I have to assume that nothing has been done. I can't believe that 115k work of ATF fluid in a transmission is a good thing. I'm not going to flush it because that could knock looks a lot of gunk too fast and cause problems. But I am going to drain and fill it over the course of several weeks to work out the gunk that I'm sure is in there.

 

I would expect this will lead to smoother shifting and longer life. But I can't imagine where leaving that old crap in there will actually be better for the transmission.

[Wang Lung]

I'm no mechanic, but I think this line of thinking is just wrong. There was a comment in the Walk-thru forum that if your car has over 100k you shouldn't do the flush, but doing it at 30k and 60k is fine. Unfortunately I have no idea what maintenance has been performed on my '05. I have a couple records, but nothing about tranny service. So I have to assume that nothing has been done. I can't believe that 115k work of ATF fluid in a transmission is a good thing. I'm not going to flush it because that could knock looks a lot of gunk too fast and cause problems. But I am going to drain and fill it over the course of several weeks to work out the gunk that I'm sure is in there.

 

I would expect this will lead to smoother shifting and longer life. But I can't imagine where leaving that old crap in there will actually be better for the transmission.

 

I agree. FWIW.

[boxman]

ATF doesn't really gunk up like you'd think, that stuff is one of the best cleaning solvents out there.

[racerj782011]

Agreed, ATF is a great solvent, but I think what they're trying to say is over time, ATF's cleaning abilities degrade. So if you have ATF with a lot of miles, solvent abilities decrease and the chance for build-up to occur is there. If you do a complete flush with new ATF, the cleaning ability is back and can knock all of that crap loose. Thus the chance for issues. Just the way I'm interpreting. Hope this helps.

[Chris GTO TT]

Right and that's why you should do a pan drain and fill at least once before you do the complete the fluid exchange. It helps to restore the cleaning ability of the fluid without having the drastic effects of completely new fluid. You should also plan on replacing the filter behind the drivers side headlight when you do the fluid exchange.