From Mark's fluid change article. Basically:

1. Repeat step 5 (which is "Run the engine until you see some air in the clear tubing. As soon as you see air shut off the engine. Refill through the dipstick tube with the same amount as you just pumped out") until you have added 19 quarts with of new ATF to the system with an E4OD or 4R100.

Wouldn't you need a lot more than 19 quarts to keep replacing the ATF you just pumped out? At what point do I reconnect the line?

I'm wanting to do this myself but fear there is a missing step.

 

Seemed to work out perfectly for me...
If I remember correctly, I got about 5-6 qts out when I dropped the pan. Re-installed the pan, add about 6 qts of fluid (Qts #1 thru 6), connect the clear tubing, run the engine until I saw bubbles and shut it off. Looked like about 6 qts that came out so I added 6 more (qts #7 thru 12) ran it again until I saw bubbles and shut the engine off. Added 6 more qts (#13 thru 18). Disconnected the clear tubing, reconnected the cooler return line. Start up the engine, get the trans to operating temp, check the dipstick which needed about 1 more qt to fill line.

Hope this helps.

 

Nope, the idea is to push the old fluid out with the new fluid. Thats why you use a few extra quarts then the trans actually takes. By pulling off the return line, you're stopping the old fluid from going back into the pan and the air bubbles show up after the new fluid level drops to the point where the pickup sucks in air. Thats when you shut off and refill the 6 or so quarts.

Does it make sense?

 

Makes better sense. Thanks.
Is there anything wrong with idling the trans dry or using a cheaper sacrificial fluid?

 

Don't let it run dry. As soon as you see air, shut it down.

There's no point in using a cheaper fluid. If done according to the instructions, you'll only waste maybe a quart or two at most since you're just replacing what you pump out. How old is the fluid in your trans? When I flushed mine, there was a noticeable color change when the new fluid started coming out (similar to when you do a power steering flush on the diesels).

 

If you idle it dry you'll have to replace the pump in the transmission.

If you want to use a cheaper sacrificial fluid make sure to run at least 20 quarts of the good stuff through the trans to make sure all of the cheap stuff is out.

 

That is how I did it, for the sake of keeping track I pumped out 4 quarts at a time...easier for me to know what went out vs. what is going in. I ended up running 20 quarts through just for safe measure but at 9.88 a gallon I can live with 2 wasted quarts.

Seriously took 20 mins...easy as pie. I have done it to two vehicles and both times it has done wonders!

 

Good idea, should work nicely. I think I'll try that next time. I have a container that I ONLY use for trans fluid changes and I think it has qt marks on it so it will work nicely.

You are right, it's super easy to do. I am glad Mark posted the write up because I never would have worked up the nerve to do my own fluid changes without his help. It's been about 25k miles since I changed the fluid last. The previous fluid had 58k miles on it and it still looked new so I wasn't sure I was doing it correctly but I just followed Mark's directions and it worked exactly as he described.

I am not sure how long I should go between changes though. I had my trans fluid sampled with about 16,500 miles of use and it looks pretty good still. I'll get it sampled again in 5k miles and see what the report looks like. Maybe change it every 45K? I tow a trailer about 4-5 times a year that weighs 16,500 lbs so the trans gets a good workout.

Here is a copy of the report in case anyone is interested in the readings.
I used Motorcraft Mercon V oil. Not sure if it's regular, syn blend or full syn...the bottle didn't say anything to indicate one or the other so I am assuming it was the standard formula. I purchased it at the Ford dealer. Seems like some very high quality stuff though, sure performs well.