Transmission Cooler Lines

This procedure covers the removal and replacement of the transmission cooler lines on a 2018-2024 Honda Accord with 1.5L turbo engine and CVT transmission.

Warnings

Tools required

Parts

• Transmission cooler line (upper) × 1 — Use OEM specification
• Transmission cooler line (lower) × 1 — Use OEM specification
• Transmission drain plug crush washer × 1 — 94109-20000 or equivalent
• Transmission cooler line O-rings × 4 — Use OEM specification

Fluids

• Honda DW-1 ATF — 2.5 qt

Preparation

1. Park vehicle on level ground and apply parking brake
2. Place wheel chocks behind rear wheels
3. Allow transmission to cool to ambient temperature if recently driven
4. Raise front of vehicle using floor jack and support securely on jack stands at manufacturer-specified lift points
5. Remove engine under cover using 10mm socket (multiple clips and fasteners)
6. Locate transmission cooler lines running from transmission to radiator on driver's side
7. Position drain pans under transmission cooler line connections at both transmission and radiator

Procedure

1. 1

   Drain partial transmission fluid
   Remove transmission drain plug using 24mm socket to drain approximately 2-3 quarts of fluid into drain pan. This reduces fluid loss when disconnecting cooler lines. Clean drain plug and install with new crush washer.
   Torque spec

   Transmission Drain Plug30 Nm (22 lb-ft)
2. 2

   Disconnect cooler lines at radiator
   Locate cooler line connections at the bottom of the radiator on the driver's side. Use 17mm flare nut wrench to loosen the upper cooler line fitting at the radiator. Use 14mm flare nut wrench for the lower line. Turn counterclockwise slowly to prevent fluid spray. Allow fluid to drain into pan. Cap or plug radiator ports with clean plastic bags and secure with zip ties.
3. 3

   Remove cooler line brackets
   Locate the transmission cooler line mounting brackets along the frame rail. Remove bracket bolts using 10mm socket. Note the routing path and bracket positions for reinstallation. Some brackets may also secure other lines or harnesses.
4. 4

   Disconnect cooler lines at transmission
   Access the transmission cooler line connections on the driver's side of the transmission case near the bell housing. Clean area around fittings with wire brush. Use 17mm flare nut wrench for upper line and 14mm for lower line. Loosen fittings counterclockwise. Be prepared for additional fluid drainage. Immediately cap open transmission ports with clean plastic bags and secure with zip ties to prevent contamination.
5. 5

   Remove old cooler lines
   Carefully extract cooler lines from engine bay, noting exact routing path, clearances from exhaust components, and any heat shielding. Take photos if necessary for reference during installation. Inspect old lines for failure points such as corrosion, rubbing damage, or kinking.
6. 6

   Prepare new cooler lines
   Unpack new cooler lines and verify correct length and fitting types match original equipment. Install new O-rings on all fittings, lightly lubricating with clean Honda DW-1 ATF. Do not reuse old O-rings. Ensure fittings are clean and free of debris or burrs.
7. 7

   Route and install new cooler lines
   Route new cooler lines along the same path as originals, ensuring adequate clearance from exhaust manifold, catalytic converter, and moving components. Lines should not contact sharp edges or create tight bend radius. Install mounting brackets loosely to allow for adjustment during final connection.
8. 8

   Connect lines to transmission
   Remove protective caps from transmission ports. Thread fittings by hand first to ensure proper engagement and prevent cross-threading. Once hand-tight, use 17mm and 14mm flare nut wrenches to tighten upper and lower fittings respectively. Tighten securely but do not over-torque aluminum threads on transmission case. Typical tightness is snug plus 1/4 turn.
9. 9

   Connect lines to radiator
   Remove protective caps from radiator ports. Thread cooler line fittings into radiator connections by hand to verify proper thread engagement. Use 17mm and 14mm flare nut wrenches to tighten fittings to snug plus 1/4 turn. Verify lines are not twisted or under tension.
10. 10

    Secure mounting brackets
    Verify cooler lines are properly seated in all mounting brackets with correct routing and clearances. Tighten all bracket mounting bolts using 10mm socket. Ensure lines do not rattle or have excessive movement when tugged by hand.
11. 11

    Refill transmission fluid
    Locate transmission dipstick or fill plug on transmission. With engine off and vehicle level, add Honda DW-1 ATF through dipstick tube or fill port. Add approximately 2.5 quarts to replace fluid lost during line replacement. Do not overfill.
12. 12

    Reinstall under cover
    Clean and reinstall engine under cover using all original clips and fasteners. Ensure cover is properly seated to prevent wind noise or damage.

Reassembly

1. Double-check all cooler line connections for proper tightness and correct O-ring installation
2. Verify cooler lines have adequate clearance from hot exhaust components
3. Ensure all mounting brackets are secure and lines cannot vibrate or rub
4. Confirm engine under cover is properly installed with all fasteners

Verification

• Lower vehicle from jack stands and remove wheel chocks
• Start engine and allow to idle. Monitor for fluid leaks at all connection points
• With parking brake applied and foot on brake pedal, shift through all gear positions (P-R-N-D-L) pausing 3 seconds in each
• Return to Park and check transmission fluid level with engine at operating temperature. Add fluid if necessary to bring to proper level on dipstick
• Perform a short test drive (5-10 minutes) including highway speeds if possible to circulate fluid through cooler system
• Re-check all connections for leaks after test drive and verify fluid level again when at operating temperature
• Inspect ground under vehicle after overnight parking to confirm no fluid seepage

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