2014 Kenworth W900 Transmission Fluid & Service Guide

The 2014 Kenworth W900 is a legendary Class 8 heavy-duty truck known for its classic styling and immense capability. Because W900s are highly customizable right from the factory, they can be equipped with several different transmissions depending on the truck’s intended vocation (linehaul, heavy haul, or vocational). However, the vast majority of these rigs are fitted with Eaton Fuller manual transmissions (such as the 13-speed or 18-speed RTLO series) or Allison Heavy Duty automatic transmissions (like the 4000 RDS).

As an ASE-certified master technician, I’ve serviced countless transmissions in these big rigs. Using the correct fluid, adhering to strict service intervals, and understanding the specific needs of your transmission are critical to keeping your W900 on the road and out of the shop.

Quick answer

Here are the standard specifications for the most common transmission found in the 2014 Kenworth W900—the Eaton Fuller RTLO-18918B (18-speed manual). If your truck is equipped with an Allison automatic or an Eaton UltraShift, verify your specific capacities and filters using your service manual or with a Kenworth dealer.

• Transmission Make/Model: Eaton Fuller (e.g., RTLO series 18-speed / 13-speed)
• OEM Fluid Spec: Eaton PS-386 Synthetic Transmission Fluid (replaced the older PS-164 Rev 7 spec). For Allison automatics, use TES 295 or TES 668 approved fluid.
• Drain & Fill Capacity: Approximately 28 pints (14 quarts) for an RTLO-18918B.
• Full Overhaul Capacity: Approximately 28 to 30 pints (14 to 15 quarts).
• Filter OEM Part Number: Standard Eaton Fuller manuals do not use a replaceable paper filter; they utilize a magnetic drain plug. If equipped with an external cooler, verify the inline filter part number with your dealer. (Allison 4000 series autos use filter kit part number 29548988).
• Recommended Service Interval: 500,000 miles for linehaul/normal duty; 1,000 hours or 50,000 miles for vocational/severe duty.

Fluid type explained

For decades, heavy-duty Eaton Fuller manual transmissions relied on 50-weight synthetic transmission oil meeting the PS-164 specification. However, Eaton introduced the PS-386 specification, which is now the gold standard for all their heavy-duty manual and automated manual transmissions (AMTs). PS-386 is a lower-viscosity synthetic fluid designed to improve fuel economy, lower operating temperatures, and provide superior gear wear protection. If you are servicing a 2014 W900 with an Eaton transmission today, PS-386 is the required fluid.

If your W900 happens to be equipped with an Allison fully automatic transmission, you must use a fluid that meets the TES 295 or TES 668 specification (such as Allison Transynd). Using standard Dexron or Mercon fluids in a heavy-duty Allison will result in premature clutch wear and overheating.

Service procedure

Servicing a heavy-duty transmission requires proper safety protocols. Always ensure the truck is parked on level ground, the parking brakes are set, and the wheels are chocked.

Drain & Fill (Eaton Fuller Manual):

1. Drive the truck to bring the transmission fluid up to operating temperature. Warm fluid drains much faster and suspends more contaminants.
2. Locate the magnetic drain plug at the bottom of the transmission case. Place a large catch pan (at least 5 gallons) underneath.
3. Remove the fill plug on the side of the case first (this prevents vapor lock and ensures you can refill the transmission once it's drained).
4. Remove the drain plug and allow the fluid to drain completely.
5. Thoroughly clean the magnetic drain plug. Inspect the magnet for excessive metal shavings. A small amount of fine metal fuzz is normal; large chunks indicate internal bearing or gear failure.
6. Reinstall the drain plug and torque to 45-50 lb-ft.
7. Fill the transmission through the side fill hole with Eaton PS-386 fluid until the fluid level is exactly even with the bottom of the fill hole opening. Do not overfill.
8. Reinstall the fill plug.

Full Exchange: Unlike passenger car automatics with torque converters, a manual Eaton Fuller does not hold vast amounts of fluid hidden in hydraulic circuits. A standard drain and fill essentially replaces the entire fluid capacity, serving as a full exchange.

Service interval

The service intervals for a 2014 Kenworth W900 depend heavily on how the truck is used.

• Normal Duty (Linehaul/Highway): When running synthetic PS-386 fluid, Eaton allows for extended drain intervals. For over-the-road highway use, the fluid should be changed every 500,000 miles or 5 years, whichever comes first.
• Severe Duty (Vocational, Heavy Haul, Off-Road): If your W900 is used for logging, heavy equipment hauling, or frequent stop-and-go city driving, the transmission is subjected to much higher temperatures and stress. In these severe duty applications, fluid should be changed every 1,000 hours, 50,000 miles, or 1 year.

For Allison automatics, severe duty intervals are typically every 2,000 hours or 50,000 miles (with filter changes every 1,000 hours), while normal duty can extend to 4,000 hours or 150,000 miles.

Common transmission problems

The 2014 Kenworth W900 is generally rock-solid, but the Eaton Fuller transmissions can develop a few specific issues over hundreds of thousands of miles:

1. Air System Leaks: Eaton 13- and 18-speed transmissions rely on air pressure for range and splitter shifts. The air lines, O-rings in the shift knob, and the slave valve on the side of the transmission are prone to leaking. If you hear a hissing sound in the cab or the truck is slow to complete a range shift, check the air system.
2. Synchronizer Wear: While the main gears in a heavy-duty Eaton are unsynchronized (requiring double-clutching or float-shifting), the auxiliary section (range and splitter) does use synchronizers. Improper shifting or failing to let the RPMs match during a range shift can prematurely wear these synchronizers, leading to grinding or gear rejection.
3. Input Shaft Wear: The input shaft splines can wear down over time, especially in heavy hauling applications. This can cause clutch engagement issues or excessive noise.
4. Oil Leaks: Output shaft seals and PTO cover plates are common areas for minor seepage. Always monitor fluid levels closely during your pre-trip inspections.

Taking care of your transmission is the key to keeping your W900 profitable. Don't skip your fluid services, and always address air leaks immediately.

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