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2000 Forester L
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79 Posts
Discussion Starter #1
I have a 1999 Forester that I want to change the transmission fluid and filter on. The filter is simple enough, but how to get all of the fluid out is my question. I know I can get a bit less than half of it out by draining the pan via the drain plug, pretty straightforward. What about the torque converter? I don't have the tools or facilities to drop the transmission.

I am not an expert on transmissions, so what I am thinking about doing might be potentially lethal to my transmission; so I need some advice from people more experienced with auto transmissions. I was thinking about just leaving the drain plug out, starting the car and putting it in gear, letting the transmission pump the rest of the oil out through the pan drain plug. With another person operating the ignition and gear selector, I would signal that person to park the transmission and shut off the car once the transmission has fluid stopped pumping out of the drain plug hole. After this, I would replace the drain plug, change the filter, and begin the refilling process.

Is this a reasonably safe idea, or am I in danger of causing catastrophic damage to my transmission? Can an auto transmission run for a few seconds with little or no fluid?
 

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2009 Forester X Premium
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3,121 Posts
Id do the 3 fill method... just drain it and refill it then drive for a few days then drain it and refill it again drive for a few more days then drain it once more install the new filter and refill it that should freshen up the fluid to almost new.
 

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Premium Member
2008 2008 2.5i-2018 XT
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13,194 Posts
Id do the 3 fill method... just drain it and refill it then drive for a few days then drain it and refill it again drive for a few more days then drain it once more install the new filter and refill it that should freshen up the fluid to almost new.
A

agree 100%
 

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none none
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9,011 Posts
Either do multiple drain and fills, or connect lines to your ATF cooler lines and put one in a container of new fluid and one in an old container and start the car. It will suck the new fluid into the transmission while pumping the old fluid out. I believe theres a writeup on how to do it right (make sure you're not pumping the old fluid into the new container etc)

If you do what you're suggesting, you'll kill the transmission very quickly as it will be running with no fluid, lubrication, or hydraulic fluid (auto's use the ATF to move valves etc)
 

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2006 Forester
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6 Posts
Seems a bad idea to run the engine at all with too little ATF in the trans.
Yesterday both the drain plug and the filter were removed, then it dripped overnight. It drained 6 quarts ('06 NT)! For the 3 drain method, this gets it a little ahead for the first drain/fill than just pulling the plug. Other posts have suggested that 3 drain/fills (without filter) will net a 90% fluid replacement. By pulling the filter the first cycle, it must be even more than 90%.
Hmm, calculations show this method nets an 80% replacement after 3 drain/fill cycles. Hmm....
 

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06 Forester
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115 Posts
so i have a question comming from the scientific standpoint:
What would be the reason to change AT fluid, diff fluids sooner than called for in the manual?
I understand doing this on hard driven, performance vehicles but a daily driver, family carrier NA forester should not need this type of service.
Has anyone who is a easy driver done any type of lab analysis on the old fluids that would justify the reason for changing frequently?
 

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2008 LL Bean (4EAT)
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4,909 Posts
... connect lines to your ATF cooler lines and put one in a container of new fluid and one in an old container and start the car. It will suck the new fluid into the transmission while pumping the old fluid out. I believe theres a writeup on how to do it right (make sure you're not pumping the old fluid into the new container etc)...
I think this could be risky. The dealers use a machine programmed to do this, the BG PF5 Power Flush and Fluid Exchange System:
BG Products, Inc.
I have studied both the home drain and the power flush alternatives, and will choose the flush at when the fluid looks like it needs changing. Subaru ATF is $7 a quart, and three home drains will take 12 quarts, $84 and a couple of hours time. And the transmission will still not be solvent-flushed clean nor have 100% new ATF.
 

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2008 LL Bean (4EAT)
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4,909 Posts
... from the scientific standpoint: What would be the reason to change AT fluid, diff fluids sooner than called for in the manual?...
There is no reason to change good ATF. Engine power, driving habits and driving conditions vary. And that is why the Owners Manual does not address the subject at all, and the Maintenance Schedule out to 137,500 miles only says I (Inspect), with two notes:
4. When the vehicle is frequently operated under severe driving conditions,
replacement should be performed every 15,000 mi.
9. The ATF filter is a maintenance free part. The ATF filter needs replacement
only when it has physical damage or if the ATF has leaked.
(Of course, the ATF filter was deleted in June 2007.)

The life of the fluid will be shorter under conditions such as hard driving, city driving, boost, and trailer towing. Severe driving conditions affecting aging of ATF are heat, power transmitted and number of shifts. Fluid that needs changing will be darkened and have a smell. Also, some people will want to change sooner than others.
 
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