Is changing ATF necessary?

I’ve noticed the topic of automatic transmission fluid coming up at times, and I have to ask whether having an ATF flush done is all that necessary? Obviously, it is recommended, but between my dad and I, we’ve driven hundreds of thousands of miles with automatic transmission vehicles, having no fluid flushes ever done. Aside from needing to change the transmission on the 1979 Buick Regal when it had probably around 150,000 miles, we’ve had no trouble with transmissions. We do check it to be sure levels are good and the color is good, but that’s honestly about it. What are the thoughts of the Car Talk community on this?


First, check the owner’s manual. You do want it says and no less. We generally recommend that you change the fluid at 25 - 40,000 mile intervals.

Generally a transmission flush is not a good idea and it is primarily a wallet flush. A proper fluid change will generally include dropping the pan and cleaning the filter (something a flush does not do).

Joe, I think this may be one of the few times the owner’s manual can sometimes be suspect. I have a friend with an 09 Pontiac G8 and the manual states the fluid NEVER HAS TO BE CHANGED. Also, my gf’s 07 Uplander recommends changing only at 100k. I wouldn’t be comfortable with either of those.

I’d skip the flushes and just change it every 30k or so.

Good practice. I would say a 50/50 chance of failure on a modern transmission under 200k without changing fluid.

In response to some of the comments, I should add that I know some more modern vehicles don’t even allow for you to check the ATF level. Some don’t even have a transmission dipstick. I admit that I’m sure the manual does have a recommended interval of service, but being unable to even check the fluid can certainly lead some people to think that it’s an area that needs little, if any, maintenance.
Also, considering some responses, it would be good to get a clarification of the difference between a transmission flush and fluid change.
I appreciate the good responses on this topic as well. It’s interesting to consider whether my dad and I have just been lucky or if we’re not alone in our views on transmission fluid.

The 70s transmissions were more robust than today’s very efficient units with tighter tolerances. All posters here will recommend regular fluid and filter changes every 30,000 miles or so. In other words, more often than most manuals recommend.

Most older cars get scrapped when the transmission fails, usually long before the engine bites the dust.

If the fluid color is brown like black coffee and there is some grit on the dipstick, it is already too late! If the color is off just slightly I would recommend fluid and filter changes.

Automatics need to be serviced every 25-30k miles, regardless of what the owners manual says. Period… When it comes to service intervals on your car, leave the owners manual where it belongs, locked in the glove box. Drop your pans, inspect and clean them to where they are spotless, change the filter, reinstall pan and refill using OEM fluid. Do this every 25-30k miles and you have properly serviced your automatic.


There is a VAST difference in transmission designs…The ones used in FWD cars work a lot harder and have less to work with, so I would follow Transman’s advise on those…But RWD vehicles usually have more robust transmissions and will tolerate a 50,000 mile or 4 year service routine without undue failure risk.

As to not changing the fluid at all there are two groups of owners; the lucky ones and the unlucky ones.
Changing the fluid on a regular basis usually has a tendency to keep you in the lucky group.

The ones posting on here with transmission problems are usually part of that group who never services the transmission; either due lack of knowledge, a don’t care attitude, or a bogus owners manual recommendation.

Agree that LUCK is the residue of PLANNING!!

I don’t care what the manual says, if it isn’t sealed, if you can check it, and if it stops looking like it looked when it was put in, change it.

I accept your lucky-unlucky angle as the best answer. But what is the direct answer to his question? No one has given one. I have a 2000 Subaru Legacy with 84K. My transmission is giving out and I need a rebuild. OK fine. I’ll do that. And given the chance to do things different, I would have done at least one complete change-out/flush/filter whatever. But I had it checked every oil change. Every time it was full, it did not smell, it had perfect clear color, there was not the slightest speck to been seen on a kleenix wipe, never pulled a tough load and never did anything dumb like shifting forward from rolling backward. Sounds like BuickGuy. So what specifically is the cause of his luck and my no-luck. No one has come up with anything other than you need to change it and after that its a matter of luck.

Joe, I think this may be one of the few times the owner’s manual can sometimes be suspect.

I agree, which is why I wrote: “We generally recommend that you change the fluid at 25 - 40,000 mile intervals.”

But what is the direct answer to his question?

There is no direct answer to that question. It is a decision that must be made by the owner. What has been offered are some facts and some opinions which may be used by the OP to make his decision.

No one has come up with anything other than you need to change it and after that its a matter of luck.

I would say there is a luck factor, but choosing to provide fluid changes and filter cleaning will change the odds.

There is no set answer to this question because every automatic transmission that has ever been made is going to be subject to a few design flaws or weak points if you want to call it that.
Many will outlast the car in spite of those flaws and changing the fluid regularly will at least stack the deck in the car owners favor, so Mr. Meehan is correct.

As to Subaru, they can be a bit different and it’s impossible to say without knowing why the transmission is giving out.
One of the differences on Subaru is that they have a final drive filled with hypoid oil, which is not the same as ATF. At times there have been problems with internal seal leakage in which the hypoid oil leaks into the ATF. Eventually the automatic transmission slips due to this or the final drive fails. In the case of the latter, this can be catastrophic if neglected long enough and may split the case open.
In theory, the car owner should notice a subtle whine in a case like this but many chose to turn the radio up a few notches.

I’m not saying this is occurring in your case; only pointing out a possibility because when I worked for Subaru I saw 4 or 5 transmissions that attained scrap iron status due to this and several of these cars only had about 30-40k miles on the clock.

When a new transmission design is finalized, about 10 production-line units are put on a special dynamometer and run until they fail…The manufacturer can tell you EXACTLY how many shift cycles the transmission can perform before failure is expected. This life expectancy is not a mystery to the manufacturer, only to the consumer…It’s called MTBF, mean time before failure (50% failure point) and virtually ALL manufactured products have been tested to determine this number. You don’t think they warranty this stuff BLIND do you? All the consumer can do is put himself in the UPPER 50% group by performing proper maintenance…BuickGuy seems content to pray for luck to see him through and Need A Horse, at 84K miles has proven my point…

That makes me think of Dirty Harry:

"You’ve got to ask yourself one question: ‘Do I feel lucky?’ Well, do ya punk??