2016 Kenworth T680 Transmission Fluid & Service

Quick answer

• Common Transmission: Eaton Fuller FRO-16210C (or similar RTLO/FRO series, verify transmission tag)
• OEM Fluid Spec: Eaton PS-386 (manual transmissions) or TES 295 / TES 668 (automatic transmissions like Allison, if equipped)
• Drain & Fill Capacity: Varies significantly by transmission model. For Eaton Fuller 10-speed, approximately 13-16 quarts. Always verify with dipstick or service manual.
• Full Overhaul Capacity: Varies significantly by transmission model. For Eaton Fuller 10-speed, approximately 18-22 quarts. Always verify with service manual.
• Filter OEM Part Number: No external filter for most Eaton Fuller manual transmissions. Automatic transmissions (e.g., Allison) will have internal filters; verify with transmission model and dealer.
• Recommended Service Interval:
  • Eaton Fuller Manual: 250,000 miles or 3 years (normal duty); 120,000 miles or 1 year (severe duty/towing)
  • Allison Automatics: Refer to Allison's Prognostics system and owner's manual; typically 75,000-150,000 miles or 36-48 months for synthetic fluids.

Fluid type explained

The 2016 Kenworth T680 is a heavy-duty truck, and as such, it can be equipped with a variety of transmissions, most commonly multi-speed manual transmissions from Eaton Fuller or automatic transmissions from Allison. The type of fluid required depends entirely on the specific transmission installed.

For Eaton Fuller manual transmissions (like the FRO-16210C, RTLO series, or similar), the manufacturer specifies their Eaton PS-386 fluid. This is a synthetic or semi-synthetic heavy-duty transmission lubricant designed to meet the rigorous demands of commercial trucking applications, offering excellent thermal stability, shear resistance, and wear protection. Using an alternative fluid that meets a generic commercial gear oil specification (e.g., API GL-1, GL-4, or GL-5) without specific Eaton PS-386 approval is not recommended and can void warranties or lead to premature wear. Always confirm the exact Eaton Fuller model and consult the owner's manual for the precise fluid specification.

If your Kenworth T680 is equipped with an Allison automatic transmission (such as a 3000 or 4000 series), the fluid requirements will be different. Allison Transmissions typically specify fluids that meet their TES 295 or newer TES 668 specifications. These are high-performance, full-synthetic automatic transmission fluids that deliver extended drain intervals, improved fuel economy, and superior protection compared to conventional ATFs. Common brands that meet these specifications include Castrol Transynd, Mobil Delvac Synthetic ATF, or аналогичные (similar) products from other reputable manufacturers. Always check the Allison nameplate on the transmission itself, as well as your owner's manual, to confirm the exact fluid specification.

Service procedure

Eaton Fuller Manual Transmissions:

Servicing an Eaton Fuller manual transmission typically involves a simple drain and fill procedure. There isn't an external filter to change. The process involves:

1. Safely lifting and securing the truck.
2. Locating the drain plug (usually on the bottom of the transmission case) and the fill plug (usually on the side).
3. Draining the old fluid completely into a suitable container.
4. Reinstalling the drain plug with a new washer if recommended.
5. Filling the transmission with the specified Eaton PS-386 fluid through the fill plug opening until the fluid level reaches the bottom of the fill plug hole or up to the full mark on the dipstick (if equipped). Never overfill or underfill.
6. Running the truck briefly and checking for leaks, then rechecking the fluid level.

Allison Automatic Transmissions:

Servicing an Allison automatic transmission is more involved. It generally requires a drain and fill and a filter change. Allison transmissions feature internal filters (main and sometimes a lube filter) that need to be replaced at specified intervals. A full fluid exchange is also sometimes performed using specialized equipment to ensure complete removal of old fluid from the torque converter and cooler lines.

1. Safely lifting and securing the truck.
2. Draining the fluid from the pan.
3. Removing the transmission pan to access and replace the internal filters (sump and / or lube filter). Ensure to use genuine Allison filters or approved equivalents.
4. Cleaning the pan and magnet, then reinstalling with a new gasket.
5. Refilling with the specified Allison TES 295 or TES 668 fluid.
6. Following the manufacturer's procedure for checking the fluid level, which often involves bringing the transmission to operating temperature and checking the level in neutral, or following the electronic fluid level check procedure (if equipped).

Service interval

Eaton Fuller Manual Transmissions:

• Normal Duty: For typical highway long-haul operations without consistently heavy loads or extreme conditions, Eaton suggests a service interval of 250,000 miles or 3 years, whichever comes first.
• Severe Duty / Towing: If the truck is consistently used for heavy hauling, off-road applications, frequent stop-and-go driving, or in extremely hot or dusty environments, the service interval should be shortened to 120,000 miles or 1 year, whichever comes first.

Allison Automatic Transmissions:

Allison transmissions utilize a sophisticated Prognostics system that monitors various operating parameters and calculates the optimal fluid and filter change intervals based on actual usage. This system provides a more accurate service schedule than fixed mileage/time intervals.

• However, general guidelines for Allison transmissions using TES 295/668 synthetic fluids typically range from 75,000 to 150,000 miles (120,000 to 240,000 km) or 36 to 48 months, depending on the application and Prognostics readings. Always consult the Allison operator's manual and the Prognostics display for the most accurate service recommendations.

Common transmission problems

For Eaton Fuller Manual Transmissions in this generation of Kenworth T680s, common problems can include:

• Shifting difficulties: This can range from hard shifting to grinding gears, often pointing to issues with the clutch, slave cylinder, shifter linkage, or potentially worn synchronizers inside the transmission. Low or incorrect fluid levels can also contribute.
• Leaking seals: Input shaft seals, output shaft seals, or even inspection plate gaskets can develop leaks over time, leading to low fluid levels and potential damage.
• Bearing wear: Growling or whining noises that change with speed or gear selection can indicate worn input shaft, output shaft, or countershaft bearings, often due to high mileage, heavy loads, or insufficient lubrication.
• Shift fork wear: Repeated hard shifting or high mileage can cause wear on the shift forks, leading to difficult engagement or even gears popping out of engagement.
• Contamination of fluid: While not having external filters, internal wear can generate metallic particles that circulate in the fluid. Regular fluid changes are crucial to remove these contaminants.

For Allison Automatic Transmissions, common issues for this era can include:

• Diagnostic trouble codes (DTCs): Allison transmissions are electronically controlled and can generate various codes indicating issues with sensors, solenoids, wiring, or internal components. These often require specialized diagnostic tools.
• Delayed or harsh shifts: Can be caused by low fluid, incorrect fluid type, faulty solenoids, worn clutch packs, or issues with the transmission control module (TCM).
• Overheating: Often due to heavy loads, restricted cooler lines, a faulty fan clutch, low fluid, or internal transmission issues. Overheating can quickly degrade fluid and damage components.
• Converter lock-up issues: Problems with the torque converter locking and unlocking can lead to poor fuel economy, excessive heat, and a feeling of