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Transmission Flush?

I’ve got a 2002 Subaru Forester with 97,000 miles on it. The dealer said I needed a transmission flush. I took it to my trusted mechanic. He said the liquid was looking brown & sent me to a transmission place he trusts. The transmission place twice asked me if I was having problems with my car. No I am not - it’s running fine. Then they asked how many miles on it.

This exchange just made me uneasy - do I really need a flush? A friend of mine says that flushes are bad for the engine. What’s the real answer here? Are they bad? Do I need one?

There are lots of discussions of this up here. You can search on them.

The short story is that you should go ahead and have your pan dropped & filter replaced. This is not a flush. This should be done about every 30K miles.

If you have never had this done before I would do it twice in quicker succession (perhaps after 5-10K this time) b/c dropping the pan won’t get all of the trans fluid out. That is what I would do.

If someone talks you into a flush, this will change out all of the fluid, but the pan & filter service should be done before the flush.

A friend of mine says that flushes are bad for the engine.

A engine flush and a transmission flush are completely different.

You do NOT need a engine flush…but tranny flushes (for automatics) are recommended. The tranny should be drained…the pan dropped and the filter replaced.

Brown transmission fluid is not a good thing. It indicates that the transmission fluid is oxydized and requires replacement. And the only way to get all the oxydized fluid replaced is to have a transmission fluid exchange service performed.


First brown is bad. Damage likely has already been done. If it is still driving OK you may get by with a fluid change. I don’t recommend a “flush” A change with cleaning/replacing the filter is better IMHO. Frankly I would suggest that you should have already done your second fluid change.

Please don’t assume that a fluid change damaged your transmission if it fails soon after a change. They often do fail soon after a change, but that is only because they have never changed it and now it is starting to show signs and they change it, only to have it fail soon after.

Changing it before would be better, but now your best bet is to change it now.

What’s the history here? What does your manual require as far as periodic maintenance? Have you kept up on it?

Brown is NOT all that bad, black would be bad, but brown is an indication that service is needed immediately, but it does not mean impending doom for the transmission.

I do not agree with flushing transmissions, I think it is a waste of money, and if not done correctly, can do more damage than good. Do have the transmission fluid changed and teh filter replaced/cleaned. This means the pan has to be dropped.

When you have this service done, make sure the mechanic uses only the specified fluid for your transmission. Your owners manual will tell you what is required.

Flush vs drain and fill.

In a drain and fill, the fluid is drained and fresh fluid is put back in, much like an oil change. With automatic transmissions only about 40-60% can be drained at any one time, so a lot of the oil fluid remains. If you follow the manufacturers recommended change interval, the fluid will always be good enough for the life of the vehicle. You can do back to back fluid changes every 5-10k miles to catch up if needed.

A flush involves disconnecting a cooling line and letting the transmission pump the old fluid into a waste container. the transmission is refilled by a machine through the port where the cooling line was disconnected at the same rate the old fluid is pumped out. In theory, this should be better. The fluid is sucked out of one end of the oil pan and filled from the other.

Old fluid is constantly being mixed with fresh fluid so it isn’t as efficient as it appears to be. It costs more because it needs a lot more new fluid because of the amount of new that gets sucked out with the old, and the machine costs money that the mechanic would like to recover. In many cases, the mechanic doesn’t drop the pan to clean out the sludge or replace/clean the filter.

Get good estimates from reputable shops and make the decision that you think is best for you.


Since your Tranny could fail at ANY time, NOBODY wants to be the last man to TOUCH it, out of fear of being blamed for the failure, which, in all likelihood, will total your car…I would have the fluid and filter changed and reassure the shop you will not hold them responsible for any problems that may or may not crop up…

Some fluids darken naturally. If it is truly burnt …it will smell burnt. It’s not always an indicator of trouble.

Get the pan service as recommended. Do a fluid exchange from there on out. If you have DIY capability, the exchange is simple through the cooler lines.

The fluid exchange myth comes from those who detect trouble, change the fluid …the trans lunches just as it was going to …naturally, the fluid change caused the failure.

Not buying everything on that web page. I don’t see who the author is or what his/her credentials might be.

Brown is not always bad and the flush systems do not get 100% of the old fluid out, though it goes get more than a simple drain and fill, but it also uses more new fluid to do it.

So many people here are so quick to condemn a transmission for the slightest discoloration of the fluid, condemn a head gasket for the slightest rise in coolant temperature, etc. Often the problem isn’t as sever as many would indicate and I like to recommend the lower cost alternatives first.

Okay keith, let’s use your logic.

Since we don’t know who you are or what your credentials might be, that means we can’t believe anything you post on this board, Or for that matter, what anyone else posts on this board. And if that’s the case, what good is this board?


Does OP no good now to tell him/her what should have been done, but it is important information to others who might read this thread.

People are all over the place on ATF replacement. I don’t think it matters as long as it is changed often enough to keep it clean and in good condition.

Several years ago, the Brothers told a man with a new expensive car who proposed to drop the fluid every time he changed the oil and add back the same quantity, that this would be acceptable if a bit of over-kill.

That is what I do. On my 2002 Sienna, when I feel like it, I pull the plug, let 3 quarts drain out, and add back three quarts. Some time ago, I changed to synthetic ATF, which took several changes to get it to a high percentage.

It may also be over-kill but it costs very little compared to a transmission failure.

This car has 165,000 miles with no tranny problems so far, though the Sienna had, according to the now deceased Sienna Club, a small number of cars which died because of a failed seal in the transmission. Yet, the service writer told me they had few Sienna transmission failures. I hope he is right.

Though I drive an automatic because my feet are large for manual transmission, I don’t totally trust them, since I have had them fail without warning before.

The Sienna does not have a filter, only a screen.