Transmission Cooler Lines

This procedure covers the removal and replacement of transmission cooler lines on a 2014-2018 Chevrolet Silverado 1500 with the 5.3L V8 and RWD configuration.

Warnings

Tools required

Parts

• Transmission cooler line set (2 lines, inlet and outlet) × 1 — Use OEM specification or equivalent
• Transmission cooler line fittings (if not included with lines) × 2 — Verify thread size and type
• Transmission drain plug crush washer × 1 — Use OEM specification

Fluids

• ACDelco Dexron VI ATF — 3 qt

Preparation

1. Park vehicle on level ground and apply parking brake
2. Place wheel chocks behind rear wheels
3. Allow transmission to cool completely if vehicle was recently operated (minimum 2 hours)
4. Raise front of vehicle with floor jack and support securely on jack stands at frame rails
5. Position drain pans under transmission cooler line connections at transmission and radiator

Procedure

1. 1

   Access cooler line connections
   Locate the transmission cooler lines running along the driver side frame rail. The lines connect to the right side of the 8L90 transmission and run forward to the radiator. Remove any protective shields or brackets securing the lines to the frame using appropriate tools. Note the routing of the lines for reinstallation.
2. 2

   Disconnect lines at transmission
   Position drain pan directly under transmission cooler line fittings on the transmission case. Using a line wrench, loosen the inlet line fitting (upper connection) first, turning counterclockwise. Allow fluid to drain into pan. Once drained, remove fitting completely. Repeat for outlet line (lower connection). Expect approximately 1-2 quarts of fluid to drain from each connection.
3. 3

   Disconnect lines at radiator
   Move to the radiator cooler connections on the passenger side of the radiator assembly. Position drain pan underneath. Using a line wrench, carefully loosen the cooler line fittings at the radiator cooler. The fittings are brass and can be damaged easily, so use steady pressure without forcing. Remove both line connections and allow any remaining fluid to drain.
4. 4

   Remove cooler lines from vehicle
   Remove any remaining clips or brackets securing the cooler lines to the frame rail. Carefully pull the lines free from their routing path along the frame. Note the position of any rubber grommets or isolators on the lines. Inspect the old lines for the failure point - common issues include corrosion at fittings, road debris damage, or cracking at bend points.
5. 5

   Prepare new cooler lines
   Compare new cooler lines to old lines to verify correct length and fitting types. Inspect all fittings on new lines for damage or debris. If lines came without pre-attached fittings, install the appropriate fittings ensuring they are seated properly. Apply a light coat of clean ATF to all fitting threads and O-rings to ease installation and prevent damage.
6. 6

   Install new lines to transmission
   Route the new cooler lines along the frame rail following the same path as the original lines. Install any rubber isolators or grommets in their original positions. Thread the inlet line (upper) fitting into the transmission case by hand first to ensure proper thread engagement. Once hand-tight, use a line wrench to tighten securely, but do not overtighten as the case is aluminum. Repeat for outlet line. Typical tightness is snug plus 1/4 turn past hand-tight.
7. 7

   Connect lines at radiator
   Route the forward ends of the cooler lines to the radiator cooler connections. Ensure lines are not kinked or contacting any sharp edges. Thread fittings into radiator cooler by hand first, ensuring proper engagement. Use line wrench to tighten fittings snug plus 1/4 turn. Do not overtighten as radiator cooler fittings can strip easily.
8. 8

   Secure lines and install brackets
   Install all frame rail brackets and clips to secure cooler lines in position. Ensure lines have adequate clearance from exhaust components, drive shaft, and suspension parts throughout the full range of suspension travel. Lines should be supported every 12-18 inches to prevent vibration damage.
9. 9

   Refill transmission fluid
   Locate the transmission fill plug on the driver side of the transmission case. With vehicle level, remove fill plug. Using a fluid pump or funnel with extension, add approximately 3 quarts of ACDelco Dexron VI ATF through the fill hole. Fluid level is correct when fluid begins to seep from the fill hole. Reinstall fill plug.
   Torque spec

   Fill Plug42 Nm (31 lb-ft)
10. 10

    Check for leaks and verify fluid level
    Start engine and allow to idle. Move shifter through all gear positions, pausing 2-3 seconds in each position, then return to Park. With engine running at idle and transmission in Park, check all cooler line connections at transmission and radiator for leaks. Shut off engine. Check transmission fluid level according to manufacturer procedure (typically checked with engine running at operating temperature). Add fluid as needed to achieve proper level.

Reassembly

1. Ensure all cooler line fittings are properly tightened with line wrenches
2. Verify all frame brackets and clips are installed to support cooler lines
3. Confirm cooler lines have clearance from all moving parts and heat sources
4. Lower vehicle from jack stands once all work is verified complete

Verification

• Start engine and check for fluid leaks at all four cooler line connections (two at transmission, two at radiator)
• Take vehicle for short test drive (5-10 minutes) to bring transmission to operating temperature
• Re-check all connections for leaks with transmission at operating temperature
• Verify transmission fluid level is within proper range using dipstick or fill plug method
• Inspect under vehicle after 24 hours of normal operation to confirm no delayed leaks have developed

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