Transmission Cooler + ATF Flush (Part 2)



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(this post is part of a series, for part 1 go here. )

Last time, we were working on getting the tranny cooler installed, we were able to choose a place where to put it, next step would be to actually connect it in series with the ATX (Automatic Transmission) and exchange the ATF (Automatic Transmission Fluid) with the new one.

Here is what it looks after the time it took me continue this guide. Little bit dusty but rock solid, it hasn’t move an inch 😉


Lets remember which tools we need

  • Ramps or Jack/Jack-stands
  • Phillips Screwdriver
  • Flat Screwdriver
  • 13 mm socket
  • 10 mm socket
  • Oil drain pan
  • Containers to hold old fluid (pro tip: use empty bottles of new fluid)
  • 10 Quarts of ATF (ATF-MV for Mazda 6, be sure to select the correct fluid type for your car!)
  • Funnel
  • Short piece of clear hose 1/2″ diameter
  • Duct Tape
  • Cable Ties
  • Hose Plastic Sleeve
  • Razor blade
  • 3 meters of 3/8 Oil Cooler Hose (1.5 m could be already included in your kit)
  • Dremel/Hacksaw
  • Matt/Blanket to lay on (avoid spills on floor too)
  • Allen Keys

ATF Flush

Here is where the interesting part starts. We need to change the ATX fluid. There are multiple ways of accomplish this procedure:

  • Go to your dealer or lub shop. Pay to do it (the sissy way)
  • Get under the car, remove oil pan plug, let it drain, replace the plug, fill the reservoir, let the car idle for a while, rinse and repeat. You do this 3 times and you have “exchanged” a part of the old oil with the new one. Although a considerable amount of old oil will remain. (the not recommended way)
  • Perform a flush, the process I followed. There are a couple of ways to do it, some of them require expensive machinery that is not available to the average DIYer (similar to what the dealer will do), or you can do it yourself using the power of your car to perform the flush for you! (the recommended way)

I will explain the process and I will include a video where I mainly got my inspiration of how to perform this flush (sadly I was too busy doing it on my own to think about filming it).


…after all voiding warranties is what we always do…


Step 1. On the Mazda 6 to access the ATX you will have to remove the intake air box. (while doing this, try to clean the engine, it looks bad when dirty…)

Underneath the air box, will be a metal bracket, that serves as a mounting point for the airbox (you can see it in the previous picture). It is held by two 10 mm bolts, please remove that as well, since will be on the way of accessing the transmission.

Step 2. Identify the following hoses. (highlighted with color for reference). The red one is pressure, it goes out of the ATX into the stock cooler. Blue is the return line, it comes from the cooler back to the ATX.

We need to replace the BLUE hose, in between we are going to plug our new cooler. Which means we are going to use BOTH coolers to cool the oil. The stock one, and the aftermarket one. In other words, the new cooler will be installed in series with the existing cooler. Double the cooler, double the…. coolness? facepalm

Here is another shot of the hose to be replaced:

Both of the nipples where this hose is attached will be used to attach the two new hoses (one from the kit, another bought)

Here is an animation I created to depict the process we will be doing.

Neat huh?

#3 in the diagram is our cooler. As you could probably be thinking some Mazda 6 already contain this cooler from the factory! namely the station wagon. Its a shame the sedan doesn’t come with it.

Step 3. Run the new hose from the cooler into the engine bay, you can accomplish this in multiple ways. Follow my example here for an easy way:

Step 4. Remove the exiting hose.

Use a pair of pliers to remove the clamp, apply enough force and move it away from the ATX body. Use twisting motion to carefully remove the hose, if you plan to keep it for later use. If you don’t care about it, you can just cut it with the razor blade (you will be replacing it with the new hoses anyways).

You might get some oil leak, be sure to use some paper towels to minimize the mess.

Step 5.  Attach the new hose to the newly available nipple. giggles

This is regularly easier said than done. It takes some force to do it and I recommend using some of the new oil as a lubricant. Take a little bit of oil with the tip of your finger and rub it in the hose end, then it will get easier to attach it.

REMEMBER before attaching the hose put the clamp in place, if you forget you will have to remove the hose (or run it from the other side ) and it is a pain to remove, could be even harder than the stock one.

Perform the same to the other end of the stock hose. (with the remaining piece of oil cooler hose)

Step 7. After hoses are attached (it’s better to do it before attaching them as I came to understand later when it was a pain to perform this step) run the plastic sleeve protectors over the hoses.

Here is the result.

The sleeve protector will help avoid any rubbing the hoses might be susceptible to while the car is running, effectively removing the risk of the hose being damaged because of vibrations.

Step 8. Now we have two hoses attached to the system. One directly connected to the transmission, the other connected to the output of the stock oil cooler (under the radiator). The later would be where our oil fluid will flow from (refer to previous diagram in step 2). We need to leave that hose disconnected, and feed to an empty bucket.

The other hose (connected to the ATX), needs to be plugged into the cooler rightmost side (while looking from the front of the car). It will look like this once connected:

That’s one side done!!

Step 9. OK, now its flush time!

Jack up the car, remove the cover under the engine, this will allow us to see the transmission oil pan and its plug (circled in green)

Another view

Step 10. Remove that sucker!

Use a 5/16 Allen key for it. If this plug has never been removed it will be tight!

Pro tip: Try to use some metal tubing for leverage, it will make it easier to apply force. “Give me a place to stand, and I shall move the earth” – Archimedes

This is how it looks after its removed and the oil is drained. Remember tho, this only removes about 3 qts of ATF, more than 5 qts still remain in the system! So we need to get into the next part to be able to flush it completely.

Step 11. Now, screw the plug back in and move to the top of the car. We need to fill the 3 qts of the red liquid back into the system.

Use your power to create a makeshift funnel with hose by opening the diameter of the hose a little bit by heating one end of the hose, then using some force while the hose is soft try to stick the funnel into the hose . Finally, secure everything together using duct tape.

Put one end of the hose where the ATF dipstick is, it serves as the inlet of the reservoir too!


Add 3 qts, this will fill the oil pan we just emptied.

I noticed the clear hose was a little bit long, so I cut it just enough to be taped in position, so that filling would be faster, easier, and without having to hold the funnel.

Look ma! No hands!

Step 12. Remember the other hose we left disconnected?  It’s time to put it into a bucket, this is where all the old oil will be dumped once we start the flushing procedure. Secure with duct tape to avoid spills.

Pro tip: mark the bucket to 8.77 liters so you will know how much you have removed from the system.

Get all the oil ready to be added into the car, remove the caps to allow the oil be ready to be poured.

Now, take some time to understand the following video where the procedure is explained! Watch it many times until you feel comfortable enough to perform it yourself.

So, this is all there is to it!! As the video detailed. The process is fairly straight forward. Take all the considerations mentioned on it.

Now in his particular case, he flushed the car twice, I’m just gonna do it once. 🙂

The process I followed was:

  1. Turn on the car. (black liquid starts to come out of the hose attached to the bucket)
  2. Quickly start funneling new liquid (using the funnel attached to the dipstick inlet).
  3. While doing step 2, get another person to cycle trough all the gears (P -> R -> N -> D ) of the car, this will move the ATF out of its hiding places.
  4. Pour down all of the remaining quarts (5 in total).
  5. Turn off the car when clean red fluid comes out of the hose (check periodically).
  6. Check fluid level to be within dipstick measurements, pour in more ATF if needed.

Step 12. Cut remaining hose to length and connect to the leftmost side of the tranny cooler.

Once everything is connected, turn the car on for a few minutes on and let it idle on Park. Let the fluid go through the new cooler. Use the 10th qt to achieve the required level on the dipstick. It will take about 1/2 quart to fill the new lines and get everything the way it should be.


Another mod performed. Another story to tell.

After you finish doing this process. Check for leaks in all the places you used a clamp. Also, take the car for a ride around the block, this will help heat the oil and it will make sure you go shift through the gears. Go back to your place and double check for leaks again. If everything is fine, put the undercover back in place.

You are done.

Pack up your tools go drive with peace of mind, your transmission is protected and it won’t blow up because of heat anymore!.

Good Job!


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