Well written article on why ANY trans flush is bad

Joined
Jul 29, 2012
Messages
362
Location
Pikes Peak region
No scientific data here... I've for the most part, had used vehicles without knowing a lot of their service history. Having heard more than a few stories about a tranny flush that caused or introduced problems, I tended to do the drain and fill a few times over 4 - 6 weeks to dilute the capacity with new fluid. That, being a Mazda that was picky about the fluid spec and quite expensive. I also believe many of those that had problems likley had older or high mileage trannys that were skipped or left too long / neglected as per any services. I do think a new vehicle / owner that follows the maint guidlines from day one is a better bet though. On our cars, we add so few miles that 'affording' these services won't be an issue. I have put less than 800 miles on my VW in the past 5 months being "safer at home" as they say. grin2 *I've never bought into the benefit or felt confident of an engine flush.
 
Joined
Dec 4, 2005
Messages
1,775
Location
Kingston
Originally Posted by ford46guy
(sorry, accidentally cross posted). GM says NO NO NO to any service other than a pan drop. (Unless you feel this is an ulterior motive :lol:) https://static.nhtsa.gov/odi/tsbs/2012/SB-10062497-7690.pdf The use of external transmission fluid exchange or flush machines is not recommended for the automatic or manual transmission. Use of external machines to replace the fluid may affect the operation or durability of the transmission. Transmission fluid should only be replaced by draining and refilling following procedures in Service Information (SI). Refer to Automatic/Manual Transmission Fluid and Filter Replacement. And even if you exchange 12 qts in a flush (using the cooler lines, no machine), since the trans in P has lots of circuits blocked off, you are lucky to exchange 1/2 the fluid. And if you do flush, don't even think of doing it without a filter change. http://www.agcoauto.com/content/news/p2_articleid/238 I recently did a pan drop/filter and was thinking of doing a fluid exchange thru the cooler. Then I read people sell those Lexus and Toyota trans with 250K and never touched any fluid. Still run like new. In the early 90s after hs I worked briefly for a neighbor in a busy NYC transmission shop. He said if everyone did a pan/filter drop at 30K he would be out of business. He also said never to flush, either you waste money or will damage the unit. Zero benefit. He also said you never exchange all the fluid. He also said trans fail after flushes because of clogged filters. He has seen many. If fluid is that contaminated that you need to be replaced it you have bigger problems. Now, with the new fluids the interval may be 60-100K.
I heard the same bs from the local chain transmission rebuilder when my old boss at Goodyear had me call around pretending to be a customer getting prices on stuff like transmission flush etc. I figure he would be out of business if everyone flushed their fluid regularly. I have a 270k mile 86 gm 2004R transmission that's been flushed every 30k since 110k, no issues, 2 other high mileage 2004R's and a 700R4, now add to that a 2005 4L60E with 200k that had original fluid and filter. Also the 270k mile trans in my cutlass I only changed the filter every second flush most times once the fluid no longer became dirty looking. Also a 2000 Cavalier 4t40e flushed at 120k, and a 99 alero 4t45e flushed at 130k (original fluid). I'm forgetting others I'm sure, these were personal vehicles and family vehicles. I'm not even counting all the ones we did at Goodyear and the other dealership's I've worked at and never had a come back. I'm calling it a myth.
 
Last edited:

4WD

Joined
Sep 21, 2010
Messages
17,969
Location
Texas
Yes … the BIL put 400k on a 4L60e doing 50k BG flushes … but that does not mean I need to do the same. He has no interest in DIY automotive PM work … and dealer does drain/fill on his newer GMC …
 
Joined
Apr 25, 2017
Messages
5,913
Location
Ohio
Originally Posted by JohnG
I did a little research and found that there is a procedure for checking the fluid level in the trans. There is a plug in the side of the trans, and when you remove it, fluid should come out. I suppose several conditions are to be met before this is done, like trans at operating temp, etc. I liken it to checking the fluid level in the rear end of the old cars I used to work on.
That seems to be a fairly common method nowadays (just like has been done on manual gearboxes, diffs, transfer cases, etc for decades). I was under the impression that this was often the back-up method on modern cars though as some have 'fluid level sensors' that the automaker's and dealers could access through their diagnostic systems.
 
Joined
Dec 19, 2013
Messages
5,884
Location
Fort Worth, Texas
The fluid diagram they used is of a 4L60E & that fluid vents from the Pressure Relief Valve & is recirculated.......The Relief Valve pops offs at @ 350 psi, You have some major issues if pressure ever reaches that! It's tough to take an article serious with technical mistakes like that!
 
Joined
Sep 1, 2008
Messages
5,337
Location
Southeast Texas
I am conservative about PM, meaning I don't needlessly over do it. My vehicles have a lot of highway mileage, and I never tow, so I have a shop do a passive flush (with a BG machine) at 100K then again at 200K. I get rid of the vehicles as they approach 300K so a third service is not necessary.

I think this strikes a good economical balance while assuring the fluid stays acceptably fresh through the years. The passive flushes have never, ever caused any problems, nor have I ever lost a trans.
 
Joined
Dec 31, 2017
Messages
9,740
Location
SE British Columbia, Canada
My local GM has a flush machine. I had two flushes done. They sell it as a way of getting the old fluid from the torque convertor and placing it with new fluid, nothing more. I guess they could do the start and stop method as well. 210,000 miles on the tranny. Currently I use the dilution method, pulling out 4 quarts and replacing it yearly. I’m planning a pan drop, magnet cleaning and filter replacement this summer.
 
Joined
Jun 15, 2010
Messages
2,098
The sad part is basically every GM dealership (and other branded dealerships) all have a flush machine. A good majority of them use the BG flush system.
 
Joined
Dec 28, 2014
Messages
1,486
Regarding flushing/exchanging machines....I think they can serve a purpose, the purpose of getting a lot of fluid out relatively easily and exchanging it. But I think you need to be careful of a few things..

1. I wouldn’t “flush” I’d exchange. And I’m pretty sure they’re the same thing anyway.

2. I wouldn’t let them sell me any type of cleaner to put into that machine and then flush/exchange. Just give me the OE fluid.

3. These machines are used a lot at independent shops and you have to be “careful” of the fluid they use. They may use a universal fluid with a modifier. I don’t want that. And the flush machines will encourage that, some will try to sell you their bulk oil and additives.

4. If you find a place that uses “fresh” OE fluid in their machines, keep in mind that those machines hold three quarts of fluid in the lines and pump of those machines. That means that whatever fluid was in that machine previously, will be dumped into your transmission during YOUR exchange. So if you own a Honda and a Mazda was serviced before you? You just got three quarts of Mazda fluid dumped into your tranny.if you go to the dealer...it might be a better situation because they use the same fluid, mostly.

5. Oh, and one more thing...you still need to change your filter at some point.
 
Joined
Jul 14, 2020
Messages
746
(sorry, accidentally cross posted). GM says NO NO NO to any service other than a pan drop. (Unless you feel this is an ulterior motive :lol:) https://static.nhtsa.gov/odi/tsbs/2012/SB-10062497-7690.pdf The use of external transmission fluid exchange or flush machines is not recommended for the automatic or manual transmission. Use of external machines to replace the fluid may affect the operation or durability of the transmission. Transmission fluid should only be replaced by draining and refilling following procedures in Service Information (SI). Refer to Automatic/Manual Transmission Fluid and Filter Replacement. And even if you exchange 12 qts in a flush (using the cooler lines, no machine), since the trans in P has lots of circuits blocked off, you are lucky to exchange 1/2 the fluid. And if you do flush, don't even think of doing it without a filter change. http://www.agcoauto.com/content/news/p2_articleid/238 I recently did a pan drop/filter and was thinking of doing a fluid exchange thru the cooler. Then I read people sell those Lexus and Toyota trans with 250K and never touched any fluid. Still run like new. In the early 90s after hs I worked briefly for a neighbor in a busy NYC transmission shop. He said if everyone did a pan/filter drop at 30K he would be out of business. He also said never to flush, either you waste money or will damage the unit. Zero benefit. He also said you never exchange all the fluid. He also said trans fail after flushes because of clogged filters. He has seen many. If fluid is that contaminated that you need to be replaced it you have bigger problems. Now, with the new fluids the interval may be 60-100K.
A fluid exchange using the transmission pump to pump it out via the cooler line while topping it up from the dipstick shouldn't cause any damage. The fluid isn't doing anything differently inside the trans than it normally does, other than leaving the vehicle from the cooler hose into the drain jug.

I've done this so many times on old 80s GM's that were way overdue for a fluid change and never had an issue. The newest vehicle I've done it on is my 2005 Silverado 4L60E. The original fluid was flushed out at 192k miles. Currently at 203k.
 

4WD

Joined
Sep 21, 2010
Messages
17,969
Location
Texas
Its the lubricity of oil that protects and ZF agrees on fresh oil.

That ZF procedure really annoys me - about as much as the price of fluids ..
A fill tube with a dipstick has hot/cold levels & instructions on the dipstick …
 
Joined
Apr 17, 2012
Messages
3,343
Location
West Michigan
It's good to remember that the transmission's pump draws from the pan. When a flush is performed, what really happens is that a good bit of your new, expensive and fresh fluid is pumped right into the drain tank. While a good bit of old fluid remains mixed in, and also in the valve body, torque converter and and actuators. On my F150, with 6R80 trans, it takes about 8-9 quarts to refill after dropping the pan. Total capacity is 13 quarts. At best, either method is a partial replacement of the fluid. Since I weld a drain plug on to the pan, it's really easy to do subsequent changes to ensure more fresh fluid.

did you weld it on the very bottom of the sump or the side? What bung did you use?
 
Top