Transmission flush or just refill?

[SilentRacer]

My cars got around 40k now and im thinking of changing the transmission fluid. From what I understand this isn't as easy as pouring out the old fluid and pouring in the new since alot of it stays in the transmission. Is the one from subaru synthetic or not? How do I go about changing it?

[Huffer]

Get any ATF that meets the Subaru specs. Get about 12 qts - you'll be doing two drain/refills in a week.

Drive car until engine reaches operating temp, then put car on stands or ramps. Undo drain bolt, let old ATF flow out. Measure how much you drained.
Reinstall drain bolt, and refill the transmission with the new fluid until you replace the amount you drained.

Drive car for a few days. Repeat the process, but also add Lubegard ATF Protectant as the last bottle.

This method does not "flush" out all the old fluid, you can continue to repeat this method until the fluid you drain is clean.

An alternative method is to run the car while draining and refilling - you have to be very careful - when the fluid that is pumping out is the same color & condition as the new fluid, shut the car off and reinstall the drain bolt.

I like my first method more, it gives me more control over the amount added, so I don't have to rely on the dipstick levels.

[PetterFan]

That really helpful Huffer... Sticky worthy, in my opinion.:smile:

[SilentRacer]

How come the subaru maintenence manuel just says to inspect the transmission oil up to 120k, never says to change it or the filter?

[Huffer]

Because the ATF in there works pretty good from factory. Maintaining the level is more important, because you'd have to work pretty damn hard to cook the ATF. Towing large boats, for example.

Obviously, you should consider replacing ATF way before 120k...

If you have an external filter, you should consider changing that also - but it's not necessary as the AT is a closed unit - the only particles in there would be particles from the AT itself, and that should only happen if the fluid level is insufficient for correct lubrication.

A good mod for an AT car that works hard is a correctly sized tranny cooler, with a temp shut-off to prevent overcooling the ATF.

[SilentRacer]

Since i already bought the filter, i guess ill take off the old one and put on the new one and just pour in like 1 bottle of oil or whatever pours out. Tks for the info btw.

[ivwarrior]

An alternative method is to run the car while draining and refilling - you have to be very careful - when the fluid that is pumping out is the same color & condition as the new fluid, shut the car off and reinstall the drain bolt.

If you're going to try a home flush with the engine running, DON'T drop the drain plug, it'll drain faster than you're gonna refill through the tiny dipstick tube. Personally, I wouldn't try it myself period, but if you must, removing the line from the tranny cooler and putting it into a pan should slow the drain rate to something safer than dropping that big drain bolt. Also, it'll do a better job of making sure fluid is circulated instead of the new just draining out the drain as you're dumping it in.

Personally, I'd advise leaving "flushes" to the shops with the machine to do it right, preferably a machine that just has a bladder with old fluid going into one side pushing the new fluid that's on the other side of the bladder back into the tranny. The machines with a pump could pump too much fluid and/or too high a pressure into the transmision.

If you're gonna DIY, just do a drain and fill with the engine off. If you don't think that's enough, do a couple back to back like Huffer suggested in the first part of the post.

[TimBeeno]

I work for a jiffy lube, and I notice that doing a "T-Tech" is the best way for doing an automatic transmission. A T-Tech is a 100% tranny flush. We hook a machine up to your transmission and flush out all the oil and put brand new fluild in. The car is running during the process so it gets everything. If you have a Jiffy Lube out there, i recommend it.

[Huffer]

I would never use a flush machine. How can you guarantee that there are no contaminants from a previous flush that won't get into your transmission?

The pressure from the machines differ also.

Oh, and about my "engine running" method - you can slow the flow outward by attaching a tube and having the tube run upwards.

No disrespect, but I wouldn't go to a Jiffy Lube for ANYTHING, not even wiper blades.

[SHOfast]

I second the not going to jiffy lube unless you want problems.


Honestly, you have 40k miles on the car. Just do a regular drain and fill type transmission service, there is no need to do a fush this soon unless you are having problems. Keep the transmission serviced regularly and you will never need to do more than a regular tranmission service for regular driving conditions.