Acura 3.0 CL / TL Automatic Transmission Fluid Cooler Install
Introduction
An automatic transmission runs cooler and tends to last longer when its fluid is given extra opportunity to shed heat before it circulates back into the gearbox. This guide covers adding an inexpensive aftermarket transmission fluid cooler, such as a Hayden OC-1677, to the first-generation Acura 3.0 CL and the closely related second-generation TL, both of which are known for heat-stressed automatics. The cooler is spliced into the transmission's return line and mounted in the airflow ahead of the radiator, so fluid heading back to the transmission is chilled first. The job is a bolt-on with no radiator coolant connections involved: you clear the battery and its trays for access, tap into the correct cooler line, plumb the new cooler in, reposition the horn out of the way, and top off the fluid. The original write-up and photographs were credited to forum member Dustbuster4. Adapted from a community writeup by klepto on AcuraZine (https://acurazine.com/forums/1g-cl-diy-faq-74/tranny-cooler-install-470677/), including corrections from the follow-up discussion.
Reference
Tools Required
- Socket and ratchet set
- Combination wrenches
- Pliers for the spring/butterfly hose clamp
- Shop rags and a small drain pan
- Side cutters or a utility knife for trimming the mounting ties
- Funnel for adding ATF
- Wire strippers and crimp connectors (only if the horn harness needs extending)
Parts Required
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Aftermarket transmission fluid cooler kit (e.g. Hayden OC-1677 or Hayden 401)
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3-4 feet of transmission cooler hose (if not supplied with the kit)
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Plastic mounting ties (usually included in the cooler's mounting kit)
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Honda ATF, roughly 1/2 quart to replace what is lost
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Short length of speaker wire (optional, to extend the horn harness)
Safety Warnings
- ⚠ Use the Honda-specified ATF for the automatic. These transmissions are sensitive to fluid type, and the wrong fluid can cause shifting problems.
- ⚠ Work on a cool engine. ATF and nearby cooling-system components can be hot enough to cause burns.
- ⚠ Catch dripping ATF on a rag and keep it off painted surfaces and off the ground.
Step-by-Step Instructions
1 Remove the battery and its trays
Disconnect and lift out the battery, then set aside its hold-down strap and the plastic tray beneath it. Unbolt the metal battery tray, which is held by four bolts, and remove the single bolt that secures the battery-cable bracket to that tray. Lift the metal tray clear of the bay. This opens up the area where the transmission cooler lines run.
2 Remove the battery-tray support bracket
Underneath the metal battery tray, a support bracket braces it in place with two bolts. It is easy to overlook because it is not obvious once the tray is out, but removing it makes a large difference: it substantially improves your reach to the transmission return line you are about to work on. Take out both bolts and set the bracket aside.
3 Identify the transmission return line
Stand in front of the vehicle, looking down into the engine bay. Two transmission cooler lines run to the radiator. The return line is the one on the right; if you trace it, it connects to the lower left corner of the radiator. The other line, on the left, runs toward the right side of the radiator and is left completely alone. Only the right-hand return line is modified in this install.
4 Disconnect and re-route the return line
Release the butterfly (spring) clamp on the return line and pull the hose off its fitting. Keep a rag handy, as a small amount of ATF may weep out, though several installers report almost none comes out at all. Route this freed hose end forward to the face of the radiator. Take out the plastic guard positioned in the gap separating the radiator from the frame of the body; this opens a clean path so the hose can pass straight through to the front.
5 Run the new cooler hose
Take the length of cooler hose supplied with the kit, or buy roughly 3 to 4 feet of transmission cooler hose if none was included. Attach one end to the fitting that the original return line was removed from. Route the free end forward to the front of the radiator, following the same path as the hose you re-routed in the previous step.
6 Reposition the horn
The horn is mounted on the front of the radiator, partly in the way of where the cooler needs to sit. Swing the right horn down and over toward the left one to clear the mounting area. Keep the two horns from resting against each other; if they touch, they buzz against one another when the horn is sounded, so drop one slightly if needed. If the harness will not reach the new position, splice in a short extension (speaker wire works well) so the connector plugs back in.
7 Connect the hoses and mount the cooler
Connect the two hoses to the cooler's fittings: the lower connection carries fluid coming from the radiator side, and the other sends cooled fluid back to the transmission as the new return line. Position the cooler on the front face of the radiator, toward the lower middle-to-right area. Secure it with the kit's plastic ties, threading them through the cooler fins and then through the radiator fins, capping the ties on the radiator side and trimming the excess. As an alternative, some owners fasten the cooler to the grille support piece ahead of the radiator.
8 Reassemble the battery area
Work back in reverse order. Refit the battery-tray support bracket with its two bolts, bolt the metal battery tray back down with its four bolts, and refasten the battery-cable bracket bolt. Set the plastic tray back in, place the battery, and secure the hold-down strap.
9 Top off the fluid and check for leaks
Replace whatever ATF was lost while the line was open; plan on roughly a half quart, using Honda ATF, which is strongly advised for these automatics. Add it through the dipstick tube and confirm the level on the dipstick rather than by counting quarts. Start the engine, cycle through the gears, recheck the level, and inspect every hose connection for leaks. Note that the cooler becoming hot to the touch after a few minutes of running is normal and expected; it is shedding heat from the fluid, just as the radiator does.
Pro Tips
- 💡 The most awkward part of the job is reaching the transmission return line. Clearing the battery, both trays, and the support bracket first is what makes it manageable.
- 💡 A Hayden 401 cooler has also been reported to fit the 99 CL 3.0 well, mounted to the grille piece in front of the radiator.
- 💡 These coolers were commonly found for around $42 shipped by searching online transmission-cooler suppliers.
- 💡 If you also do a drain-and-fill on the transmission, only the accessible fluid (about 3 quarts) drains out; the torque converter and other passages retain fluid, so a partial refill is normal. Verify by fluid level, not quart count.
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