This procedure covers the removal and replacement of transmission cooler lines on a 2015-2020 Ford F-150 with the 3.5L EcoBoost V6 engine, including fluid recovery and refilling.

Warnings

Tools required

Parts

• Transmission cooler lines (set of 2) × 1 — Use OEM specification
• Quick-disconnect fittings (if damaged) × 2 — Use OEM specification
• Transmission pan gasket (if resealing) × 1 — Use OEM specification

Fluids

• Motorcraft MERCON LV ATF — 3 qt

Preparation

1. Park vehicle on level ground and engage parking brake
2. Allow engine and transmission to cool completely for at least 2 hours
3. Raise front of vehicle and secure on jack stands at frame contact points
4. Remove engine skid plate if equipped (four 13mm bolts)
5. Place drain pan under transmission cooler line connections at radiator
6. Take photos of cooler line routing for reference during reinstallation

Procedure

1. 1

   Disconnect radiator end cooler lines
   Locate the two transmission cooler lines connecting to the passenger side of the radiator. Clean the area around the quick-disconnect fittings with a shop rag. Using the appropriate quick-disconnect tool, press the release collar and pull the cooler line straight out from the radiator fitting. Repeat for the second line. Allow fluid to drain into the pan.
   ⚠Pull lines straight out to avoid damaging the quick-disconnect mechanism inside the radiator fitting.
2. 2

   Remove cooler line bracket bolts
   Locate the transmission cooler line brackets along the frame rail and near the transmission. Remove the 10mm bolts securing the cooler lines to these brackets. There are typically 2-3 brackets along the routing path. Keep track of bolt locations and any spacers or grommets.
3. 3

   Disconnect transmission end cooler lines
   Position drain pan under the transmission cooler line connections at the transmission case (driver side). Use the quick-disconnect tool to release each fitting. On the 10R80 transmission, these fittings are located on the left side of the case near the pan. Pull lines straight out and allow residual fluid to drain completely.
   ⚠Additional fluid will drain from the transmission case openings. Keep drain pan in place.
4. 4

   Remove old cooler lines
   Carefully remove the cooler lines from the vehicle, noting the routing path, clip positions, and any protective shields or heat guards. Check the routing against your reference photos. Inspect the quick-disconnect fittings on both the radiator and transmission for damage or debris.
5. 5

   Inspect and clean fittings
   Inspect the quick-disconnect fittings at the radiator and transmission for damage, corrosion, or debris. Use a wire brush to clean the external threads and sealing surfaces if necessary. Check the O-rings inside the radiator and transmission fittings - replace if damaged. Wipe all connection points clean with shop rags.
   ℹ️Do not allow dirt or debris to enter the open transmission ports. Cover with clean shop rags if needed.
6. 6

   Prepare new cooler lines
   Unpack new transmission cooler lines and verify they match the old lines in length, fitting type, and configuration. Check that all quick-disconnect fittings are intact and O-rings are properly seated. Apply a small amount of clean MERCON LV ATF to the O-rings on the line ends to aid installation.
7. 7

   Install cooler lines to transmission
   Starting at the transmission, insert each cooler line straight into the transmission case fitting until you hear and feel a distinct click. Gently pull back on each line to verify it is locked in place. The line should not pull out with moderate force.
   ⚠Ensure lines are fully seated. An incomplete connection will cause fluid leaks and potential transmission damage.
8. 8

   Route and secure cooler lines
   Route the cooler lines along the frame rail following the same path as the original lines, ensuring proper clearance from exhaust components, driveshaft, and steering linkage. Install the cooler line brackets and secure with 10mm bolts. Ensure lines are not kinked, twisted, or under tension.
9. 9

   Connect cooler lines to radiator
   Insert each cooler line into the radiator quick-disconnect fitting, pushing straight in until you hear and feel a positive click. Gently pull back on each line to verify engagement. Ensure the upper and lower lines are connected to their correct ports (refer to reference photos).
   ℹ️The supply and return lines must not be reversed. Verify routing matches original configuration.
10. 10

    Add transmission fluid
    With the vehicle still raised, locate the transmission fluid dipstick (if equipped) or fill plug. Add approximately 2-3 quarts of Motorcraft MERCON LV ATF to replace the fluid lost during line replacement. On vehicles without a dipstick, fluid must be added through the fill plug on the transmission case.
11. 11

    Check for leaks - initial inspection
    With the drain pan still positioned under the cooler line connections, start the engine and allow it to idle. Immediately inspect all four connection points (two at radiator, two at transmission) for leaks. If any leaks are observed, shut off the engine immediately and reseat the affected connection.
    ⚠Do not leave vehicle unattended during initial leak check.
12. 12

    Cycle transmission and recheck fluid
    With the engine running and parking brake engaged, shift the transmission through all gear ranges (P-R-N-D and back to P), pausing 2-3 seconds in each position. Return to Park. Check the transmission fluid level according to the procedure for your specific model year (dipstick or level plug). Add fluid as necessary to bring to the proper level.

Reassembly

1. Reinstall engine skid plate if equipped, tightening 13mm bolts in a criss-cross pattern
2. Lower vehicle from jack stands
3. Verify all tools and drain pans are removed from under vehicle

Verification

• Start engine and verify no leaks at all four cooler line connections
• Test drive vehicle for 10-15 minutes, allowing transmission to reach operating temperature
• After test drive, recheck transmission fluid level with engine running and add if necessary
• Perform final visual inspection of all cooler line connections and routing for leaks or interference
• Monitor transmission performance for proper shifting and temperature over the next few days

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