My S60R has over 170,000 miles on it and as I have done this before with success, I feel that it is important to keep the fluid clean. There are many schools of thought on trans fluid, and I do not want to get into the debate. I have personally found on all my vehicles that the best method is the drain and fill method. This involves different method for each vehicle but is pretty simple on the S60R's with the AW55 Automatic Transmissions.
Supplies Needed:
-2-3 gallons of ATF Fluid (Valvoline MaxLife is a favorite of most and within spec)
-Empty Container with measurement marks (2L)
Tools Needed:
-Drain Pan
-Funnel with Extension (this one worked good for me)
Step 1 - Remove the drain plug and drain all the ATF fluid from the transmission pan. Drain plug is a 24mm socket and has a crush washer on it.
Once the drain plug is removed you need to clean it, since it is magnetic. Pay attention to the particles on the drain plug. Anything too big may be of concern. A small build up on tiny metallic particles is to be expected.
Once all the fluid is drained, replace the drain plug and tighten. Then measure the amount of fluid that came out of the transmission. Using a filler funnel add clean ATF fluid into the dipstick hole equal to the amount that drained out. Replace the dipstick.
Then install the 1/2" OD tubing into the transmission cooler line as shown below. Be careful not to break the green tabs when removing the cooler line.
Run the tubing into a container marked with a 2-liter line. Now start and idle the car until the 2-liter line is reached, keep in mind there will be fluid in the hose that can count towards the 2 liters if it is emptied into the container.
Once you have emptied 2 liters then turn off the car, refill new fluid (2 liters) through the transmission dipstick hole (yellow dipstick), replace the dipstick and then repeat. You can repeat this as much as you like, preferably until you get a see through red colored ATF. Once done, connect all the lines back up to the transmission cooler and add the remaining 2 liters back to the transmission. Lower the vehicle off the jacks, run it, cycle it through all gears, and then check the fluid level again. MAKE SURE THE CORRECT AMOUNT OF ATF FLUID IS ADDED. A lot of people's trans problems can be linked to incorrect amount of ATF fluid.
I also added Sea-Foam Trans Tune (Hydra Trans Tune) to mine, it's hard to tell if it helps or not, but a lot of people swear by it, and I have ran it before with no ill-effects.
ALTERNATIVE METHOD: If you have the time and really want to do a better flush you can drive the vehicle between flushes as long as you make sure there is enough fluid in the transmission.
VIDA: Reset Transmission Fluid Counter in VIDA (Vida Thread Here)
YouTube videos on the process (not mine)