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To flush or not to flush...the transmission fluid, that is

I have a 2002 Chevy Cavalier sedan with 94,500 miles. It has never had any type of maintenance done to the transmission and is running smoothly; no apparent shifting issues. Recent visits to the shop for other issues have brought up the discussion of having the transmission fluid flushed and filled. The mechanic brought out a card with a sample of my fluid on it; it is definitely quite dark in color, not the usual red/purple of fresh transmission fluid. However, I have heard and read several stories about people who have their transmission fluid flushed and refilled, only to have their transmission fail a short time later. I’ve talked to friends who are car savvy only to get very differing opinions. Some say do the flush; some say have the pan dropped, replace the filter, and top off the fluid only; still others say do nothing since there are no apparent problems with the transmission. I cannot afford to have my transmission fail, whether caused by the flush or by failure to do any type of service. Any advice/experience is appreciated.

The pan should be dropped and cleaned, the filter changed, and the transmission flushed AFTER those 2 things have been done.

Flushing is often blamed for causing a transmission problem when the odds are that a problem was looming anyway.
In your particular case, you state the fluid is quite dark in color and that is not a good sign. Dark fluid usually means aged, burned fluid and contaminated fluid due to friction material.

Dropping the transmission pan allows the person doing the service to inspect the bottom of the pan and note if there is an excessive amount of sludge or particles which could point to a problem at some point in the future.

I’m with @OK4450 on that. Since the fluid was dark, however, and never changed, I would drain and change the filter, clean out the pan, and then do the same again in 5000 miles or so.

I would just drain, clean pan, replace filter and refill. I don’t like the flushing on OLDER transmissions. The dirt can be flushed and forced into the valve body and cause failure down the road.

Here’s the deal, a flush or fluid exchange by itself is taking the old fluid from one cooling line and putting fresh fluid into the other where it is dumped into the pan full of old fluid. This does not get all the old fluid out as all you are doing is continually diluting what’s in the pan.

If you drop the pan, clean it out and clean or replace the filter, the refill the pan with fresh fluid, then hook up the fluid exchange machine, you will completely replace more of the fluid. The torque converter holds so much ATF that it too is just continually diluted. Modern transmission don’t have a drain plug in the torque converter anymore, if they did, there would be no reason for the flush or fluid exchange machine.

However, if you drain and refill on a regular schedule, even though you only get about half the old ATF out, that is enough to keep the transmission going for the normal service life of the car. The fresh additives and fresh fluid from a half exchange is all it needs to keep it going.


Actually, unless things have changed in the 5 years since I left the dealership, Mercedes-Benz vehicles have a torque converter drain plug

I don’t run in those circles. More like run of the mill, mass market type vehicles.


The Dodge Charger, and some other Dodges too, still use a 5-speed Mercedes-Benz automatic transmission. I’d be willing to bet $5 that the owners don’t know that

I’m not sure if all of the Chargers use it, but some of them do, including the police pursuit

I never recommend a fluid flush on a transmission. The old “drop the pan and replace the filter” has always worked for me through the years. The flush and fill technique was devised to make the process quicker and to increase the bottom line of the repair shop. It was not devised because automatic transmissions needed it or would be benefited in any way by the procedure.

I’m afraid of flushing and would just drop the pan, clean it and change the filter, then do it again in a month or two. I had this discussion with the trans shop I deal with and they agreed that flushing has more to do with profits for the shop than good service techniques for the customer, and didn’t recommend it.

Agree with missileman. The flush was invented not because of any real mechanical need, but as a way for shops to make more money. Automatic transmissions did perfectly well for 40+ years before the flush machine, as long as they were properly maintained. And if they aren’t a flush isn’t going to help.

I agree with @missileman and @Bing. No flushing.

Include me with @Docnick and @OK4450 as two good ways of looking at delayed maintenance.
Flushing if done correctly is the only way to remove or dilute ALL of the old transmission fluid at one time. If the transmission has never been serviced for nearly 100k miles, you are definitely living on borrowed time. Just draining and refilling leaves a significant amount of very old fluid in there. So, you have two options IMO. Flush and refill completely, or drain and refill but do it again well within the recomended interval, perhaps in the next 5 to 10 k miles. IMHO, it makes not a whit of difference. Though personally, if I were doing it myself, two to three drain and refills and a short drive between each would accomplish the same thing.

I had my transmission flushed and changed at 60 k miles but 30k later, I just had a drain and refill. If you do it like you should, every 30 k miles, drain and refills are fine. If you wait like you did and like I did, you create problems like making these types of decisions. I am not experienced with auto transmissions enough to be aware of any differences personally as the cars I have now are the first autos I have ever had.

But, no mechanic I have talked to personally feels diffentley then I have stated? Flushing IMHO, is not invented to make more money, but may be worth it in your case. It’s over maintenance if you change regularly but worthwhile in some situations. People who are afraid of it ? I don’t know what to say. To think that accumulated sludge or metal fillings or old tranny fluid is all that hold your trans together and flushing it all out will destroy it, is beyound my feeble little mind to comprehend.

@dagosa, I’m no expert, but at least one mfr (Honda) advises against flushing in any circumstance.

Another reason for the flush was to stop ham fisted quicke oil change employees from stripping pan bolts or drain plugs.

Sounds like avoiding the flush in favor of dropping the pan/changing the filter is the way to go! Thank you all for sharing your advice and experience! :slight_smile:

If you read my entire post, you’d see there is an option. You need to make up as best you can for poor transmission maintenance by removing or diluting as much fluid as possible. You don’t change fluid for 100 k miles ? At least, give it two proper changes in short order. OP thinks it’s an either or situation like changing the filter and dropping the an is not part of a proper flush…not true.

@dagosa…I’m personally not afraid of transmission fluid flushes in the least. The thing that scares me is the overwhelming number of “technicians” out there that do this procedure incorrectly. In my experience…it’s most of the shops out there that are doing flushes. Some shops can do flushes properly with the proper equipment but they are too few and far between.

What I do: Drop the pan, change the filter and then change as much as you can siphon out of the dipstick every oil change, which amounts to be about a pint. You can siphon it out (get the siphon at Dollar General) while you’re draining the motor oil, and it adds another 5 minutes to your routine maintenance. I started doing this a few years ago with our only AT car, and now the fluid looks great whenever it is checked, the transmissions shifts really nice, and I have no worries about the AT. Cheap and easy. Rocketman

Hey, Daisy,
I was in almost the exact same situation you are in a couple of months ago with my ‘98 Cavalier. I just dropped the pan, drained, cleaned, and changed the filter out. In my opinion, (take it at face value-I only have about five years’ experience. MANY more knowledgeable than me.) I think a drain and refil will be fine for you. Hope I helped,