Replace the transmission cooler lines that route transmission fluid from the transmission to the radiator-mounted cooler, preventing leaks and maintaining proper fluid temperature.

Warnings

Tools required

Parts

• Transmission cooler line set (inlet and outlet) × 1 — BC3Z-7A031-A or equivalent
• Transmission cooler line O-rings (if not included with lines) × 4 — Use OEM specification
• Push-connect retaining clips (if damaged) × 4 — Use OEM specification

Fluids

• Motorcraft MERCON LV ATF — 2 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine and transmission to cool completely (minimum 2 hours after operation)
3. Raise and support vehicle securely on jack stands at manufacturer-specified lift points
4. Remove plastic skid plate or underbody panels if equipped to access transmission cooler lines
5. Locate transmission cooler lines running from transmission to radiator cooler on passenger side

Procedure

1. 1

   Prepare workspace and identify line routing
   Position drain pans beneath the transmission cooler line connections at both the transmission and radiator. Take photographs or mark the routing of existing lines to ensure correct installation of replacement lines. Note which line is the inlet (from transmission to cooler) and which is the outlet (from cooler to transmission). The upper line at the transmission is typically the inlet.
2. 2

   Disconnect cooler lines at radiator
   Use the appropriate quick-disconnect tool to release the cooler line fittings at the radiator-mounted transmission cooler. Insert the tool into the fitting and push inward while pulling the line away from the radiator. Allow fluid to drain into the pan. Inspect the O-rings remaining in the radiator fittings and remove them with a pick tool. Clean the radiator fitting ports with a shop rag.
3. 3

   Disconnect cooler lines at transmission
   Locate the cooler line connections on the right side of the 10R80 transmission case. Use the quick-disconnect tool to release each fitting from the transmission. Push the tool into the fitting while pulling the line away from the case. Allow remaining fluid to drain completely into the pan. Keep the disconnected lines elevated to minimize fluid loss.
4. 4

   Remove mounting clips and brackets
   Trace the cooler lines along their path and remove any mounting clips, brackets, or ties securing the lines to the frame, crossmember, or body. On 2015-2020 F-150 models, there are typically 2-3 rubber-isolated clips along the passenger frame rail. Note the exact position of each clip for reinstallation. Remove the old lines from the vehicle.
5. 5

   Inspect fittings and clean connection points
   Examine the transmission case fittings and radiator cooler ports for damage, debris, or corrosion. Use a wire brush to clean any corrosion from the metal fittings. Inspect the quick-connect retaining clips; replace if damaged or deformed. Ensure no debris enters the open transmission or cooler ports by stuffing clean shop rags into the openings temporarily.
6. 6

   Prepare new cooler lines
   Unpack the new transmission cooler line set and verify both inlet and outlet lines are included. Install new O-rings onto each end of both lines, lubricating them lightly with clean MERCON LV ATF. Ensure O-rings are properly seated in their grooves. Verify that quick-connect retaining clips are properly installed on each line end.
7. 7

   Install cooler lines to transmission
   Remove the shop rags from the transmission fittings. Starting with the lower outlet line, align the line with the transmission fitting and push firmly until you hear and feel a distinct click indicating the quick-connect has engaged. Tug on the line to verify it is locked in place. Repeat for the upper inlet line. Ensure lines are not twisted or kinked.
8. 8

   Route lines and install mounting hardware
   Route the cooler lines along the frame rail following the path documented earlier, maintaining proper clearance from the exhaust, driveshaft, and suspension components. Install the mounting clips and brackets in their original positions, ensuring the lines are supported but not over-tightened to allow for thermal expansion. Verify at least 1 inch clearance from all moving parts and heat sources.
9. 9

   Connect cooler lines to radiator
   Remove shop rags from the radiator cooler fittings. Align each cooler line with its corresponding radiator fitting (match inlet to inlet, outlet to outlet). Push each line firmly into the fitting until it clicks into place. Pull on each line to verify secure engagement. Ensure the lines have smooth bends with no sharp kinks between the transmission and radiator.
10. 10

    Add transmission fluid
    Remove the transmission dipstick and insert a funnel. Add 1.5 to 2 quarts of Motorcraft MERCON LV ATF to replace fluid lost during line replacement. Do not overfill at this stage. Reinsert the dipstick. This initial fill prevents running the transmission dry during the next step.
11. 11

    Check for leaks and purge air
    With the vehicle still raised and supported, start the engine and allow it to idle. Immediately check all four connection points (two at transmission, two at radiator) for leaks. With the engine at idle and brake applied, shift through all gear positions, pausing 2-3 seconds in each position, then return to Park. This purges air from the cooler circuit. Shut off the engine and recheck all connections for leaks.
12. 12

    Set final fluid level
    With the engine off, check the transmission fluid level on the dipstick. The level should be in the cold range. Add additional MERCON LV ATF as needed to reach the proper cold level. After a test drive and the transmission reaches operating temperature (160-200°F), recheck the fluid level and adjust to the hot range on the dipstick. The 10R80 transmission requires precise fluid level for proper operation.

Reassembly

1. Reinstall any underbody panels or skid plates removed during access
2. Lower vehicle from jack stands and perform final ground-level inspection
3. Dispose of used transmission fluid at an appropriate recycling facility

Verification

• Start the engine and visually inspect all cooler line connections for leaks with the engine running
• Test drive the vehicle for 10-15 minutes to bring transmission to operating temperature
• Recheck fluid level with transmission at operating temperature and adjust as needed to hot range on dipstick
• Perform a final inspection of all connections after test drive, looking for any seepage or wet spots
• Verify smooth transmission operation through all gear ranges with no delayed engagement or slipping

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