2025 Kenworth T680 Transmission Fluid & Service

Quick answer

• Transmission Make/Model: Eaton Endurant XD / XD Pro Series (automated manual transmission)
• OEM Fluid Spec: Eaton PS-386 synthetic transmission fluid (or equivalent meeting Eaton PS-386 specification)
• Drain & Fill Capacity: Approximately 16.5 – 18.5 quarts (15.6 – 17.5 liters) depending on model and cooler size.
• Full Overhaul Capacity: Approximately 20.0 – 22.0 quarts (18.9 – 20.8 liters) depending on model and cooler size.
• Filter OEM Part Number: Verify with Eaton or Kenworth dealer, as specific part numbers can vary by transmission variant and production year.
• Recommended Service Interval:
  • Normal Duty: 500,000 miles (800,000 km) or 4 years, whichever comes first.
  • Severe Duty / Towing: 250,000 miles (400,000 km) or 2 years, whichever comes first.

Fluid type explained

The 2025 Kenworth T680, when equipped with an Eaton Endurant XD or XD Pro Series automated manual transmission (AMT), requires a specific synthetic transmission fluid that meets the Eaton PS-386 specification. This proprietary specification ensures the fluid provides optimal lubrication, thermal stability, and wear protection for the sophisticated internal components of the Endurant AMT.

Eaton PS-386 fluid is engineered to handle the high temperatures and pressures common in heavy-duty trucking applications, providing extended drain intervals and improved fuel efficiency. Using fluids that do not meet the PS-386 specification can lead to premature wear, shifting issues, and potential transmission damage, voiding warranties.

Always confirm the fluid type and specification in your owner's manual or service guide, or consult with a Kenworth or Eaton dealer to ensure you are using the correct fluid for your specific transmission configuration. While there may be aftermarket fluids that claim to meet PS-386, it's generally recommended to use genuine Eaton PS-386 fluid for the best performance and longevity.

Service procedure

Servicing an Eaton Endurant XD/XD Pro transmission typically involves a drain and fill procedure. Unlike traditional automatic transmissions, AMTs like the Endurant do not have a torque converter and often use a simpler drain and fill method for fluid replacement. A full fluid exchange, while possible, is less common and usually reserved for significant repairs or overhauls.

Drain & Fill:

1. Preparation: Park the truck on a level surface, engage the parking brake, and block the wheels. Allow the transmission to cool to a safe handling temperature.
2. Locate Drain Plug: Place a suitable drain pan with adequate capacity under the transmission. Locate the drain plug on the bottom of the transmission housing.
3. Drain Fluid: Carefully remove the drain plug and allow all the old fluid to drain completely. Inspect the fluid for excessive debris or metallic particles, which could indicate internal wear.
4. Replace Drain Plug: Once drained, reinstall the drain plug, ensuring a new washer (if specified) is used and tightened to the manufacturer's torque specifications.
5. Locate Fill Plug: Locate the fill plug on the side or rear of the transmission.
6. Refill Fluid: Using a fluid pump, slowly add new Eaton PS-386 compliant fluid through the fill opening until it begins to seep out of the fill hole. This indicates the correct level for a drain and fill.
7. Reinstall Fill Plug: Reinstall the fill plug, ensuring it is tightened to specification.
8. Check for Leaks: Start the engine and check for any leaks around the drain and fill plugs.

Filter Replacement: The Eaton Endurant XD/XD Pro transmissions are designed with internal filtration that is generally not a user-serviceable item during routine fluid changes. The filter is typically designed to last the life of the transmission under normal operating conditions or is replaced during a major overhaul. Always verify filter serviceability and replacement with the official Eaton service manual or a certified technician.

Capacity Notes: The drain and fill capacity will be less than the full overhaul capacity because some fluid will remain in the transmission's internal passages and cooler lines. Always refer to the specific capacity listed in your truck's owner’s manual or the Eaton service manual, as variations can occur based on the exact transmission model, cooler configuration, and driveline setup.

Service interval

Adhering to the recommended service intervals is crucial for the longevity and optimal performance of your Kenworth T680's Eaton Endurant transmission. The intervals are categorized by duty cycle:

• Normal Duty: For vehicles operating in typical long-haul, on-highway conditions without consistent heavy loads or extreme terrain. The recommended interval is 500,000 miles (800,000 km) or 4 years, whichever comes first.
• Severe Duty / Towing: This applies to trucks consistently hauling maximum gross vehicle weight (GVW), operating in stop-and-go traffic, extreme hot or cold climates, hilly or mountainous terrain, or any application involving frequent or heavy towing. For these conditions, the service interval is reduced to 250,000 miles (400,000 km) or 2 years, whichever comes first.

It's important to monitor for signs of abnormal transmission behavior regardless of the service interval. Early detection of issues can prevent more costly repairs down the line.

Common transmission problems

The Eaton Endurant XD/XD Pro series AMTs are generally robust and reliable, but like any complex mechanical system, they can encounter issues. For the generation found in the 2025 Kenworth T680, some common areas to be aware of include:

• Shifting Performance Issues: These can manifest as rough shifts, delayed engagement, or difficulty shifting into certain gears. Often, these can be related to sensor malfunctions (speed sensors, neutral sensor), clutch actuator problems, or software calibration issues. While fluid quality is paramount, the electronic control unit (ECU) and associated sensors play a significant role in shift quality.
• Fluid Leaks: Although rare for a new transmission, leaks can develop around seals, gaskets, or cooler lines over time. Regularly inspect for any signs of fluid weeping or dripping under the truck.
• Clutch Wear: As an AMT, the Endurant relies on a clutch for engagement. While designed for long life, aggressive driving, frequent heavy loads, or improper calibration can accelerate clutch wear, leading to slipping or engagement issues. The clutch actuator also needs to be in good working order for proper operation.
• Actuator Malfunctions: The Endurant uses various actuators (e.g., shift actuators, clutch actuator) to perform its functions. Malfunctions in these components can directly impact shifting, gear engagement, or overall transmission operation.
• Diagnostic Trouble Codes (DTCs): Modern AMTs are heavily reliant on electronics. Any internal or external sensor fault, communication issue, or electrical problem can trigger a Diagnostic Trouble Code, illuminating the check engine or transmission warning light. Prompt diagnosis using proprietary diagnostic tools is essential.

Many common issues for modern AMTs are often electrical or software-related before they are mechanical failures, emphasizing the importance of proper diagnostics by trained technicians. Regular maintenance and using the correct fluid are your best defenses against transmission problems.

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