Transmission Oil Cooler

Replace the transmission oil cooler on a 2007-2013 Mercedes-Benz S65 AMG with M275 6.0L V12 BiTurbo engine to resolve leaks or cooling efficiency issues.

Warnings

Tools required

Parts

• Transmission oil cooler × 1 — Use OEM specification
• Transmission cooler line O-rings × 4 — Use OEM specification
• Transmission drain plug crush washer × 1 — Use OEM specification
• Cooler mounting hardware kit × 1 — Use OEM specification if damaged

Fluids

• Mercedes-Benz ATF 134 — 10 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow transmission and engine to cool completely (minimum 2 hours after operation)
3. Raise and secure vehicle on jack stands at manufacturer-specified lift points
4. Remove engine undercover panels using 10mm socket
5. Place drain pan beneath transmission drain plug location
6. Disconnect negative battery terminal to prevent accidental electrical shorts

Procedure

1. 1

   Drain transmission fluid
   Locate the transmission drain plug on the bottom of the transmission pan. Using a 13mm socket, carefully loosen and remove the drain plug. Allow fluid to drain completely into drain pan (expect 8-10 quarts). Inspect the magnetic drain plug for excessive metal debris which could indicate internal transmission wear. Remove and discard the old crush washer from the drain plug.
   Torque spec

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

   Access transmission oil cooler
   From under the vehicle, locate the transmission oil cooler mounted in front of or beside the radiator assembly. Remove the front bumper lower air dam if necessary for improved access using 10mm fasteners. The cooler is typically positioned on the driver's side of the radiator with two feed and return lines.
3. 3

   Disconnect transmission cooler lines
   Identify the inlet and outlet cooler lines connected to the transmission oil cooler. Use the appropriate oil cooler line disconnect tool to release the quick-connect fittings. If equipped with threaded fittings, use a 16mm line wrench to prevent rounding. Have a drain pan ready as residual fluid will drain from the lines. Cap or plug open lines immediately to prevent contamination.
   ⚠Mark or photograph line positions before disconnection to ensure correct reassembly. Reversed lines will cause transmission damage.
4. 4

   Remove mounting hardware
   Using a 13mm socket, remove the transmission oil cooler mounting bolts. The S65 AMG typically uses two or three mounting bolts securing the cooler to the radiator support or chassis bracket. Support the cooler with one hand while removing the final bolt to prevent it from falling.
   Torque spec

   Mounting Bolts37 Nm (27 lb-ft)
5. 5

   Remove old transmission oil cooler
   Carefully extract the transmission oil cooler from its mounting position. Work slowly to avoid damaging radiator fins or nearby coolant hoses. Tilt and rotate as needed to clear any obstructions. Once removed, drain any remaining fluid into the drain pan and inspect mounting surfaces for debris or damage.
6. 6

   Prepare new transmission oil cooler
   Unbox the new transmission oil cooler and verify all mounting bracket positions match the original unit. Install new O-rings on all cooler line connection points, lubricating them lightly with clean ATF 134. Inspect the new cooler for any shipping damage or debris inside the cooler passages. Do not remove protective caps until ready to install.
7. 7

   Install new transmission oil cooler
   Position the new transmission oil cooler into the mounting location, ensuring it seats properly against mounting brackets and does not contact the radiator. Align mounting holes and hand-thread mounting bolts to prevent cross-threading. Verify cooler orientation matches the original installation before tightening.
   Torque spec

   Mounting Bolts37 Nm (27 lb-ft)
8. 8

   Connect transmission cooler lines
   Remove protective caps from cooler fittings. Connect the transmission cooler lines to the correct inlet and outlet ports on the new cooler, referring to your installation photos. For quick-connect fittings, push firmly until you hear/feel a click. For threaded connections, hand-tighten first, then use a line wrench to snug. Do not overtighten as this can damage the cooler ports.
   ⚠Ensure O-rings are properly seated and lines are connected to correct ports. Reversed flow will cause inadequate cooling and potential transmission overheating.
9. 9

   Reinstall drain plug
   Clean the drain plug threads and transmission pan drain hole with brake cleaner. Install the new crush washer onto the drain plug. Thread the drain plug by hand into the transmission pan until seated, then torque to specification using a torque wrench.
   Torque spec

   Transmission Drain Plug30 Nm (22 lb-ft)
10. 10

    Refill transmission fluid
    Locate the transmission fill plug or use the dipstick tube depending on your specific transmission variant. Using a transmission fluid fill pump, add approximately 8 quarts of Mercedes-Benz ATF 134. Fill slowly to allow air to escape. The 7G-Tronic transmission in the S65 requires precise fluid level, so add conservatively and check level with engine running at operating temperature.
    ℹ️The 7-speed automatic transmission requires fluid level check with transmission at operating temperature (176-194°F) while running through all gear positions.
11. 11

    Check for leaks and verify installation
    Reinstall undercover panels. Start the engine and allow it to reach operating temperature. With the engine running and parking brake engaged, shift through all gear positions (P-R-N-D-S) pausing 3 seconds in each position. Return to Park. Inspect all cooler line connections and the cooler itself for any signs of leakage. Check transmission fluid level according to manufacturer procedure and add fluid as necessary to bring to proper level.

Reassembly

1. Reinstall all undercover panels and secure with original fasteners
2. Reinstall front bumper air dam if removed during access
3. Reconnect negative battery terminal
4. Lower vehicle from jack stands
5. Dispose of used ATF fluid properly at a recycling facility

Verification

• Start engine and verify no transmission fluid leaks at cooler connections after 5 minutes of idle
• Test drive vehicle for 15-20 minutes, ensuring transmission shifts smoothly through all gears
• After test drive, recheck transmission fluid level at operating temperature and adjust as needed
• Inspect cooler area again for leaks after test drive while engine is still warm
• Verify transmission temperature gauge shows normal operating range (typically 180-200°F)
• Monitor transmission fluid level and condition over the next few days of driving

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