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I found this on another site I frequent. This is from someone who tests transmissions for a major manufacturer. He talks about fluid replacement, filter replacement and flushes. The thread is here:
http://www.corner-carvers.com/forums/showthread.php?t=44014
It's post #25 from a user called: crosser

And I'll paste the text here:

We do have a person like that and I'm right here. I have been in transmission calibration, testing and hardware development for a little over 10 years. I'll try my best to summarize all the posts prior to this since quoting so many will be difficult. I’m also going to try and keep it simple and will make some generalizations based on normal use in passenger cars. Maybe in time this will be “THE OFFICIAL TRANSMISSION FLUID THREAD”.

Let’s start with transmission fluid life span. What determines the life of transmission fluid is the temperature profile over time. If you keep the transmission around the normal operating temperature (about 90 C) most of the current fluids can last about 125K miles. When I say current, were talking about vehicle from around 1998 forward. The more time the transmission is over the normal operating temperature you start to reduce it’s life span. If the transmission sump temperature reaches over 140 C continuously, you can bet pretty much plan on changing the fluid with in days. On a typical hot test trip lasting about 2 weeks where we continuously hit sump temperatures around 140C + the fluid is pretty much done.

So far I’ve only mentioned sump temperatures. There can be localized hot spots in the transmission, like the clutch friction surfaces. In these areas the fluid can flash to extremely high temperatures over 230 C. So a transmission that sees a lot of shift events even though the sump temperature was never that high can also require a fluid change early in its life.

ATF and most of the Dexeron/Mercon used to be red. There are some yellow and blue versions out there as well but in the end they all can turn brown with age. As many have said, if it smells burnt, the fluid is done. Burnt fluid will not lubricate parts as effectively or carry heat away from the clutches as effectively. Burnt smelling fluid can be caused by a number things (slipping clutches, heavy towing, long brake stalls) regardless it needs to be changed to keep your transmission happy for many miles to come.

Particulate in the fluid can come from two places. Clutch material break down or metal wear. Usually you will not see metal particles in the oil on the dipstick (if the transmission has one) until the magnet in the pan if completely covered. If you see them on the dipstick when checking the fluid level, get ready for a failed transmission, soon. Clutch material is basically made of paper, so it pretty much stays suspended in the oil. Worn clutches can cause a burnt oil smell, usually because they are slipping and generating excessive localized heat. It’s actually quite hard to see the clutch particulate in the oil. Most transmission fluids appear brown when there is a lot of clutch friction material floating around. I have pulled apart transmissions from durability vehicles that still had bright red fluid in them even though they had 125K miles. I have also pulled apart similar transmission that were functioning with in acceptable limits for 125K miles with brown fluid and the clutch packs were fine and with in the allowed tolerance. The difference was the cycle they were on. The one with fresh fluid was on a test cycle were it saw very little temperature cycling. The brown one had a lot of temperature cycling but never exceeded 100 C. The difference was more moisture accumulated in the one transmission causing the fluid to change color.

So color alone won’t tell you if the fluid is bad, but it is a good indicator. Smelling the fluid is a better measure, if it even smells slightly burned it should be changed sooner rather than later.

What I haven’t covered yet is the friction modifiers added to transmission fluid. Automatic transmissions need special oil. It has to lubricate bearing, gears and sliding parts, it has to act as a cooling medium for the clutches but it cannot lubricate the clutches to the point where it diminishes the coefficient of friction. The balance of lubrication, cooling and maintaining the clutch friction material is difficult. Time and heat will deplete the friction modifiers which keep the clutches happy. Once these are gone clutch temperatures start to go up and the wear accelerates.

Transmission fluid changes should always be accompanied by a fresh filter. That is probably stating the obvious but I have seen quite a few people not realize that since the functionality of automatic transmissions is not very common knowledge. Through testing we’ve determined that under normal use most people can go about 120K miles with out a fluid change. Depending on use that number can go down, but it’s a good rule for refreshing the fluid in a passenger car. Over time the clutch and metal particles can build up and start to cause problems for the valve body. Even though transmissions have a filter they are not designed to catch really small particles and the magnets in the sump can only retain so much. If enough of these particles build up around the valves in the valve body you can destroy a transmission in short order. A sticking valve can cause a few clutch slip events and then it’s time for a rebuild.

One more thing to address, flushing the transmission versus just draining and refilling it. Yes a fluid flush can get more of the used oil out of a transmission and as was stated you “run” the transmission in many cases to do it. I’ve seen some repair shops do this instead of changing the fluid since they cannot access the filter with out removing the transmission. I don’t feel a fluid flush is any better than just changing the fluid and filter. A flush has a couple of risks. One is that if the transmission pump is run dry it can damage the pump, this is the equivalent of liver cancer for a transmission. It will die in time. There is a theory that a flush can stir up all the contaminates settled in the bottom of the pan depending on how they introduce the new oil. If they pull the pan, clean it, install a new filter then the contaminate thing is not an issue but you still run the risk of running the pump dry if not done properly. In my opinion and based on my experiments with durability cars, just changing the fluid is fine. I was doing shift quality studies over the life of a transmission and decided to see what happened if I threw some fresh fluid in at the end of its life. The shift quality was worse until the transmission could adapt to compensate for the new slip characteristics of the clutches with fresh fluid. The shift times did improve a little but the shift feel was pretty much back to my findings with the old used up oil.

If the filter is accessible, change it with the fluid and don’t worry about the residual oil in the torque converter. A transmission flush just doesn’t have much benefit versus the risk and cost.

In summary most transmissions can go about 100K on the original fluid give or take some mileage and depending on use. If you live in hotter climates or in the mountains, they could require a change around 80K or less. Add in towing and it could be even less depending on what temperatures the transmission reaches.
 

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so my 50K fluid change intervals might be overkill, but i'd rather have peace of mind and added insurance against a premature failure... :)
 
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Most of us van owners were aware of this from older chrysler products lol. My van gets it once a year, maybe 10k miles. Yes it is overkill, but I beat my van to death AND my trans is a junkyard special that's gotten 17k miles so far and has one mild issue (mild slipping feeling when heavy throttle in first gear or reverse, been that way from the get go so its not gonna fail anytime soon imo).
 

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Sounds like he was talking about ATF+3 fluid which would make this outdated info.
 

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Sounds like he was talking about ATF+3 fluid which would make this outdated info.
He's talking atf+4 and similar fluids from other brands. The guy was lumping all brands into a general time frame. If one were to run atf+3 for 100k+ miles, that would not fare well for the trans. Chrysler themselves knew that +3 was good for 30k and +4 is good for 100K per their service manuals. Unless the vehicle sees severe use which most fall into (interestingly enough, my hard use still meets the normal service interval schedule lol).
 

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well what are the procedure to replacement of the fluid in a 6 speed transmission? removal of cover and all. can it be done by a normal mechanical inclined person. only issue i have is the refill? unless im able to collect all the fluid and measure it and thats if i dont loose any. i think dealer got us going back to them?
 

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They make a dipstick you can buy at the dealer as the 6 speed does not come with one. Should be all you need extra compared to a more conventional trans with the dipstick already there.
 

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Good post from someone who knows that a pan-drop, clean pan and magnet, replace filter and gasket and re-fill is much superior to a "flush"
 

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well what are the procedure to replacement of the fluid in a 6 speed transmission? removal of cover and all. can it be done by a normal mechanical inclined person. only issue i have is the refill? unless im able to collect all the fluid and measure it and thats if i dont loose any. i think dealer got us going back to them?
To change ALL of the ATF, I use the procedure outlined by James Bottger here. Helps to have two people for the part where you are having the tranny pump the old fluid out while you are adding new. If well prepared, you can do this in an hour or less. Use a big plastic tub to collect the fluid being removed and pour it into some old empty 1 gallon oil jugs to measure how much was removed. If you do a 100% fluid change with ATF+4, you should easily get 60K miles out of this fluid. If you dont have an aux tranny cooler, put one of these in first, then change the fluid. This is cheap insurance for your transmission.
 

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Doing just a pan drop every 60k will be sufficient unless the old fluid is burnt. The full replacement is nice, but not necessary.
 

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To change ALL of the ATF, I use the procedure outlined by James Bottger here. Helps to have two people for the part where you are having the tranny pump the old fluid out while you are adding new. If well prepared, you can do this in an hour or less. Use a big plastic tub to collect the fluid being removed and pour it into some old empty 1 gallon oil jugs to measure how much was removed. If you do a 100% fluid change with ATF+4, you should easily get 60K miles out of this fluid. If you dont have an aux tranny cooler, put one of these in first, then change the fluid. This is cheap insurance for your transmission.
Unfortunately, unless you drop the pan, you are not changing the filter out.
 

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Unfortunately, unless you drop the pan, you are not changing the filter out.
The procedure I referenced does involve dropping the pan. In fact, the first part of of the procedure amounts to a typical "drop the pan" fluid and filter change. Once you've done that and topped it of with fluid (this only gets about 4 qt), you hook up a clear hose to the tranny output and let it pump the fluid out as you add new fluid in the dipstick tube until the fluid you see coming out of the clear tubing look like new fluid (or you can do it by volume).
 

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The procedure I referenced does involve dropping the pan. In fact, the first part of of the procedure amounts to a typical "drop the pan" fluid and filter change.

You drop your pan when performing a "flush", but most dealers/servicers will not, so the pan/magnet never gets inspected and cleaned and the old fiter remains, possibly dis-lodged.
 

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I don't advocate flushes which do not include a pan drop and filter change even if it's the dealer performing the work.

Sent from my Droid using Tapatalk
 

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Do dealers do the pan drop, replace filter thing, or only do flushes? I asked once but they did flushbecause I didn't make sure they understood what I wanted. (old 3rd gen van)
 

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A dealer will do a pan drop, it is usually considered a standard trans service vs. a flush.
 

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some will do a flush. Just because it's a dealer does not mean they don't buy in to the whole flush thing.

I had a dealer suggest a flush once. I declined.
 
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