Or is it a good idea? When I say total change, I mean changing as much of the fluid as I can by removing the cooler line and have it going to a bucket while pouring in new ATF while the engine is running- after I drop pan and replace filter. No flush chemicals, additives or "force flush" machine will be used. Transmission is a 4T40 in a Olds Alero. So good idea or bad?
Is doing a complete ATF change a real bad idea?
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As long as the fluid can be poured in at the same rate so that the pump isn't starved of fluid.I can't do this on mine ,It just wont flow in fast enough.I have to pump out about 3/4 of a gallon and then replace.
I think it's a great idea to do the full exchange. I would drop and clean the pan and change the filter also.
I recently had all this done on my Ford and it improved significantly. While researching the whole process, I discovered that what you described above was the recommended procedure (but with multiple steps to ensure it was done safely).
Dropping the pan is important to allow you to inspect everything more closely eg the magnet. If you find that the system was particularly dirty, you may want to consider doing another full exchange several thousand miles later as the new fluid may end up performing a lot of cleaning.
In that case, you may want to get some cheap ATF for this change, and then refill later with some higher quality full synthetic ATF.
And remember to buy the exact spec of ATF for your vehicle. Don't buy anything multi purpose.
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A fluid flush is a poor idea I think, if the AT has lots of miles on it. A fluid exchange is probably a good idea.
It's a good idea if executed properly. Not too difficult, but can be a bit messy. I had the output tube flop out of the bucket when I was doing a Honda Accord. Not a huge amount of old ATF escaped, but still.
Amsoil ATF will work great in the 4T40 in the Alero. If your fluid is fairly shot, you will have a noticeable improvement with fresh fluid.
Originally Posted By: Eddie
A fluid flush is a poor idea I think, if the AT has lots of miles on it. A fluid exchange is probably a good idea.
I replaced the OEM transmission fluid on my 98 Camry @ 100k miles with Mobil 1 synthetic "multi purpose" formula. Tranny instantly started shifting MUCH better, esp in cooler weather. I did a second and 3rd drain n fill a few days and 100 miles apart. Shifted almost flawlessly. Couldn't feel the shifts half the time, esp the higher gears.
@ 160k i did 2 more regular drain n fills with M1 Synthetic tranny fluid (new formula now)
The Camry is now @ 210,00 miles and i swear it shifts just as smooth as it did when it had 45,000 miles on it. Tranny fluid is Pink as can be but i still plan to keep changing it @ 60k intervals to keep things clean and fresh and continue the amazing shift quality for as long as possible.
This time i'm going with Amsoil ATF, (again, a multi vehicle formula, which i also use in my 2007 Civic EX 5spd Auto with excellent results)
I might consider dropping the pan to finally clean the magnet after almost 15 years of service but with such good performance out of the transmission, i might keep doing regular drain n fills until the car is retired after 300k miles and replaced with something new 
For what it's worth here is what I do.
drop the pan every 60,000 miles to change filter, every 30,000 miles I drain and replace the fluid 3 times. I run the car and the trans while up on stands for 10 minutes moving carefully through the gears.
Important on your first drain measure what has come out, record that volume for future reference, and replace with your new ATF. I'm getting 80% to 90% of the old atf depending on which vehicle I'm doing. to get into the high 90% you need to repeat 5 to 6 times. Since Dex-VI and MercV are supposed to be good for 100,000 miles then the old fluid left in has more life especially after being fortified by the new fluid.
That's my seat of the pants analysis!
Wow I spent $75 on the fluid for one exchange. How much are you spending to do 3 drains when really 1 would be fine?
I believe there are techniques for exchanging all the fluid which only use a quart or two more than the capacity. Essentially you let all the old fluid run out while adding and pushing it out with new fluid. When the fluid runs out fresh, you've gotten out virtually 100% of the old fluid.
No need to do 3 full drain and refills when doing regular changes. Doing a couple a few hundred miles apart might make sense if the transmission had been previously neglected.
Originally Posted By: exranger06
Originally Posted By: Eddie
A fluid flush is a poor idea I think, if the AT has lots of miles on it. A fluid exchange is probably a good idea.
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Originally Posted By: rjacket
Some garages / machines use pressure to exchange ie flush the fluid backwards, supposedly to clean it.
Originally Posted By: CLeming
Or is it a good idea? When I say total change, I mean changing as much of the fluid as I can by removing the cooler line and have it going to a bucket while pouring in new ATF while the engine is running- after I drop pan and replace filter. No flush chemicals, additives or "force flush" machine will be used. Transmission is a 4T40 in a Olds Alero. So good idea or bad?
Originally Posted By: RF Overlord
Originally Posted By: rjacket
Some garages / machines use pressure to exchange ie flush the fluid backwards, supposedly to clean it.
While I have never actually seen one of the reverse flush machines personally, there have been references to them in various literature. I have never cared enough to do any research because I did my own fluid exchanges, but I had occasion to talk to Abe Khalil (the Khalil of Eleftherakis and Khalil, the two engineers that did so much research on ATF and wrote so many great SAE white papers on the subject) spent a great deal of time condemning those machines and describing in detail the harm they did. So they exist, or at least existed. Maybe their faults led to their demise in the past few years.
I agree wit RF Overlord above about the "ATF change that kills transmissions" and rjacket about dropping the pan before doing a fluid exchange.
I will repeat my mantra yet again that dropping the pan for the first change is the most important pan drop because all the break-in and manufacturing contamination will be in there. Remember that 75 percent of the total lifetime contamination of an automatic will come in the first 5000 miles due to break in and manufacturing. Once that period is passed and the fluid filtered or changed, the contamination levels (mg/mile) drops massively.
Somebody else had another explanation. If the transmission has moderatr clogs in it and if the cleaner is too aggressive, it could dislodge larger chunks and could block critical passages which were not completely blocked before. I personally do not know if just exchanging the fluid adds so much cleaner to cause this kind of problem but it does sound feasible.
Originally Posted By: Vikas
Somebody else had another explanation. If the transmission has moderatr clogs in it and if the cleaner is too aggressive, it could dislodge larger chunks and could block critical passages which were not completely blocked before. I personally do not know if just exchanging the fluid adds so much cleaner to cause this kind of problem but it does sound feasible.
I think its more due to shops not wanting to be on the hook for a transmission that might be on its way out.
Originally Posted By: Jim Allen
Originally Posted By: Donald
I think its more due to shops not wanting to be on the hook for a transmission that might be on its way out.
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Originally Posted By: Jim Allen
I will repeat my mantra yet again that dropping the pan for the first change is the most important pan drop because all the break-in and manufacturing contamination will be in there. Remember that 75 percent of the total lifetime contamination of an automatic will come in the first 5000 miles due to break in and manufacturing. Once that period is passed and the fluid filtered or changed, the contamination levels (mg/mile) drops massively.
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