Transmission Cooler + ATF Flush (Part 1)


in ,

(this post is part of a series, for part 2 go here. )


Automatic transmissions are extremely vulnerable to heat. The additional size and number of moving parts creates more heat, which requires additional fluid capacity, and cooling. The Mazda 6 ATX (Automatic Transmission) takes 8.77 qts or 8.3 liters.

If an ATX’s temperature is running a bit higher than nominal, its fluid reservoir degrades faster. If the fluid is not being replenished regularly, this results in a degradation of protection, and eventual complete failure of the fluid’s ability to protect the moving parts within the transmission, resulting in greatly reduced longevity of the ATX. A mere 15F change can result in the transmissions lifespan being reduced by half.

Automatic transmissions which begin overheating also have other problems as well. Shifts become inconsistent, sometimes slipping or hesitating. The tranny can feel sluggish, and shift with poor performance.

Here’s an excellent article on How Automatic Transmissions Work, and why such a large amount of heat is both produced, and MUST be removed.


Increased frequency of fluid changes combined with the installation of an aftermarket transmission cooler will greatly increase the transmissions longevity, as well as providing for more consistent shifts and better shifting performance.  Adding an in-line transmission filter (serviceable vs the non serviceable stock one) will extend the transmissions life far beyond the warranty, possibly matching the engine for longevity purposes.

Transmission Cooler Types

Of the two, the stacked plate design is both more efficient, and lighter. Certain designs such as those from B&M and Hayden are stacked plate designs which also feature low pressure drop protection, and a viscosity-based thermostat.

So off to the race…what exactly is this installation going to entail? Well, there are two primary steps: installing the cooler and draining/refilling the tranny. Optionally, you can also install an inline filter. I will cover this in a separate article later.

Parts and tools

  • Ramps or Jack/Jackstands
  • 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 fuild)
  • 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
  • Duct Tape
  • Cable Ties
  • Hose Plastic Sleeve
  • Razor blade
  • Tranny cooler kit (Kit used in this guide, amazon has them cheaper)
  • 3 meters of 3/8 Oil Cooler Hose (1.5 m could be already included in your kit)
  • Dremel/Hacksaw
  • Black Engine Paint
  • Matt/Blanket to lay on (avoid spills on floor too)
  • Allen Keys

Make sure to start this mod when you have an extra day free after you begin.  Starting on a Friday or a Saturday would be great, if you had sat/sun free.  Though this mod can be performed in a few hours, if any difficulties should arise, it would be useful to have an additional day to iron them out, vs having to call in sick to work on Monday.


This guide is geared towards Mazda 6 owners, although you can apply most of the principles to other make and models, just make sure to find the respective places, bolts, and hoses, for your car.

Tranny Cooler Installation

Step 1. Remove your car grille.

This will allow you to find a suitable spot to mount your cooler, I will use the bolts used to hold the hood latch as a base. The bolts (circled in green) can be removed with a 10 mm socket.

Step 2. Choose your spot:

As you can see, this position will be perfect to hold the cooler. This is also the recommended place to put the cooler according to the kit’s installation instructions (in front of radiator). This will maximize air flow going to the cooler.

Step 3. Use the Engine Paint to turn your mounting brackets black.

Step 4. Bolt everything in place.

As a recommendation make a mark where the hood latch is currently in place, this will help you, if you later remove it, to be able to leave it in the same position as before. Or, as I did, just remove one bolt at a time, and fit the mounting bracket under it, tight  it down, then move to the next one. If you fail to replace the latch in its previous position, you will have problems opening and closing the hood.

Make sure not to strip the screws, but also ensure a tight fit.  Use a lock washer behind the mounting bracket before the nut.  You can also cut down the bolts if you feel so inclined. I also added a small piece of foam in between the brackets and the cooler itself.  (To ensure no rubbing occurs).

Step 5. Use the included zip ties to hold the bottom part of the cooler.

Doing this will allow to avoid the cooler vibrate or move when the car is running. I used the bumper frame to do this. Here is another angle:

After this step is done, all that’s left is to run the cooler lines.


We have completed the first step of the guide. Please join me in the next part where we will be connecting the hoses and flushing the existing ATF with the new one.


Leave a Reply

Your email address will not be published. Required fields are marked *