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I believe my Automatic Transmission fluid needs a' changing. I have a 1994 legacy with just about 100k miles, and I don't think the ATF was ever changed. Now the reason I think the fluid needs changing is because sometimes the car takes to long to switch into the highest gear (especially when the weather is cold). Sometimes I can be driving on the highway (at about 60 mph) for upwards of 10 miles before the transmission will switch into the highest gear.

I called the local Subaru dealer and the mechanic told me that for my car I don't need an ATF flush and fluid replacement, rather all that needs to be done is to let out some of the old fluid and then replace (with new fluid) what was let out.

I have experience working on cars but I have never changed transmission fluid, and I have heard it can be rather tricky, and if done wrong can screw up the transmission.

So, here are my two questions.

1) Do I need to change my transmission fluid?, and if so should it be done as the local Subaru dealers mechanic suggested.

2) Is doing a partial transmission fluid replacement (as the local Subaru dealers mechanic suggested) a DIY type of job? (any advice would be most helpful!!).

you tubes bro its easy. There is a drain plug on the tranny pan. If you do not have a service manual such as haynes or chiltons then I highly recommend getting one.

Yeah, partial drain and fill is done exactly the same as an oil change. Just be wary of accidentally draining the front diff instead of the trans (or you could drain and refill both). And the dealer gave you good advice, you don't want to do any kind of trans flush service on the cars.

To echo what the others have said, yes you can replace the ATF fluid yourself. I highly recommend against a flush, especially on a transmission that hasn't had the fluid changed regularly. The drain plug for the ATF is on the driver's side of the transmission pan. The drain plug on the passenger side is for the front diff.

Try and get an idea of how much fluid is drained out so you can refill the appropriate amount. 3.5-4.5 qts is probably in the ball park of what is drained for a typical drain & fill. However, sometimes on the older cars the anti-drain back valve on the torque converter is bad and the fluid will drain out of the torque converter. This could increase the amount of fluid drained to 5-6 qts.

When adding fluid back in, it's better to error on the side of too little than too much. You will need to fill the fluid back in through the ATF dipstick. I would recommend getting a transmission filler funnel. To properly check the ATF level, the engine MUST be running and preferably at normal idle speed. While parked on a flat surface and engine running, slowly cycle the gear selector from park to 1 and back to park again. Leave the engine running and then check the ATF level. Initially, try and get the level in between the two COLD marks. Once you're in the ball park, go drive the car for 5-10 miles to get the fluid up to temperature, then recheck the level against the HOT marks. Add any additional fluid as needed.

Other thing to note, what you are experiencing with the transmission not shifting into the high gear when the transmission is cold is NORMAL behavior and by design. This is done to heat up the transmission fluid to normal operating temperature more quickly.

Other thing to note, what you are experiencing with the transmission not shifting into the high gear when the transmission is cold is NORMAL behavior and by design. This is done to heat up the transmission fluid to normal operating temperature more quickly.

So, before I go about trying to figure out how to do an ATF drain and fill, I would like to be certain that my car requires this. As I said before, my legacy has just about 100k miles, and I don't think the ATF was ever changed. Also in colder weather while driving on the highway (at about 60 mph) the transmission won't switch into the highest gear until I've driven for quite a while, sometimes over 10 miles.

Do any or all of these factors mean I need to do a partial ATF drain and fill?

Have you checked the ATF? As long as its still red/pink and doesn't have a burnt appearance or smell, and is at the right level, its safe to say its not the cause of any problems.

As far as warming up, when my car was 4eat I found that incredibly annoying. Wastes a ton of gas if your commute involves driving 45mph or more. But depending on the exact temperature it will take kinda long sometimes. Keep in mind that the ATF is cooled by the radiator, so if your coolant isn't up to temp yet it will take longer for the ATF to warm up. I found it helped a lot to let the car warm up for a few minutes before my drive.

Does it shift into 4th normally once its warm? If so, there likely isn't a problem with that either. I'm not sire if the trans temp sensor is ever known to need replacing.

James614 wrote:Have you checked the ATF? As long as its still red/pink and doesn't have a burnt appearance or smell, and is at the right level, its safe to say its not the cause of any problems.

As far as warming up, when my car was 4eat I found that incredibly annoying. Wastes a ton of gas if your commute involves driving 45mph or more. But depending on the exact temperature it will take kinda long sometimes. Keep in mind that the ATF is cooled by the radiator, so if your coolant isn't up to temp yet it will take longer for the ATF to warm up. I found it helped a lot to let the car warm up for a few minutes before my drive.

Does it shift into 4th normally once its warm? If so, there likely isn't a problem with that either. I'm not sire if the trans temp sensor is ever known to need replacing.

I couldn't smell anything the last time I checked the ATF, and the color was pinkish/red. I will try and check it again to be sure.

Even if it's low miles, the age of the ATF should be taken into consideration. Even if it's not the cause of your problems I'd suggest replacing it for peace of mind.

mike-tracy wrote:Even if it's low miles, the age of the ATF should be taken into consideration. Even if it's not the cause of your problems I'd suggest replacing it for peace of mind.

So, is there any reason not to do a partial ATF drain and fill?
I have heard that messing with the ATF can cause all sorts of problems.

Flushing an older tranny is usually what causes the problems, not draining and refilling. Is there a 1,000,000% guarantee that anything you do to the tranny won't in some way affect it? Of course not. But in my opinion, and from experience, partial draining is the least invasive thing you can do to see if the fluid is the cause.

I wasn't suggesting you shouldn't do a drain and fill, just that it likely won't fix any problems. But its good preventative maintenance regardless. There is no reason not to do it