2016 Peterbilt 579 Transmission Fluid, Capacity, & Service Guide

As an ASE-certified master technician who has spent countless hours turning wrenches on heavy-duty rigs, I know firsthand that maintaining the transmission in a Class 8 truck like the 2016 Peterbilt 579 is the key to keeping it on the road and out of the shop. The 2016 Peterbilt 579 is a staple in linehaul and regional trucking, most commonly equipped with an Eaton Fuller automated manual transmission (AMT) such as the Eaton Fuller Advantage or UltraShift Plus, though manual 10-, 13-, and 18-speeds, as well as Allison automatics, are also out there.

Whether you are an owner-operator pulling 80,000 pounds daily or a fleet maintenance manager, knowing the exact fluid specs and service intervals for your driveline is essential to preventing catastrophic failures. Here is your comprehensive guide to servicing the transmission in a 2016 Peterbilt 579.

Quick answer: 2016 Peterbilt 579 Transmission Specs

Please note: The following specs apply to the most common Eaton Fuller Heavy-Duty Automated/Manual setups. If your truck is equipped with an Allison automatic (e.g., 4000 HS/RDS), your specs will differ (requiring TES 295 / TES 668 fluid).

• Transmission make/model: Eaton Fuller Advantage AMT, UltraShift Plus, or Eaton Heavy-Duty Manual (10, 13, or 18-speed)
• OEM fluid spec: Eaton PS-386 Synthetic Transmission Fluid
• Drain & fill capacity: Approximately 28 pints (14 quarts), but varies slightly depending on the exact transmission model, PTO presence, and cooler size. Always check the transmission data tag.
• Full overhaul capacity: Approximately 28 to 30 pints (14 to 15 quarts) for a dry fill.
• Filter OEM part number: Most Eaton heavy-duty manual and AMT transmissions do not utilize a traditional spin-on fluid filter for routine maintenance; they use an internal magnetic strainer. (If equipped with a cooler/filter loop or an Allison automatic, verify the exact filter part number with your dealer or service manual).
• Recommended service interval: Up to 500,000 miles (Linehaul / Normal Duty) or 180,000 miles / 3 years (Severe Duty / Vocational).

Fluid type explained

For the 2016 Peterbilt 579 equipped with an Eaton Fuller transmission, the gold standard—and the OEM requirement—is Eaton PS-386 Synthetic Transmission Fluid.

Introduced to replace the older PS-164rev7 specification (often associated with Roadranger SAE 50), the PS-386 fluid is a specialized synthetic lube designed to improve fuel economy, lower operating temperatures, and provide superior gear wear protection. It is specifically formulated to handle the high torque loads of modern PACCAR MX-13 and Cummins ISX15 engines. Using standard off-the-shelf gear oil or outdated specs can lead to harsh shifting, rapid synchronizer wear, and voided warranties.

If your 579 is equipped with an Allison transmission, you must use a fluid that meets the TES 295 or newer TES 668 specification (such as Allison TranSynd) to ensure the life of the torque converter and internal clutches.

Service procedure

Servicing a heavy-duty Eaton transmission is decidedly different from servicing a passenger car automatic. There are no fluid exchange or "flush" machines used here.

Drain and Fill: The service procedure for the Eaton AMT or manual is a straightforward drain and fill. Always ensure the truck is parked on level ground. Clean the area around the drain and fill plugs to prevent dirt from entering the gearbox. Remove the fill plug first (located on the side of the case) to ensure you can refill it, then remove the lower drain plug. Allow the gear oil to completely drain. Heavy-duty synthetic gear oil is thick, so draining it when the transmission is warm (but not scalding hot) will help carry away suspended contaminants.

Inspect the magnetic drain plug for excessive metal shavings. A fine paste is normal; large metal flakes indicate an impending mechanical failure. Reinstall the drain plug and fill the transmission through the side port until the fluid is level with the bottom of the fill hole. Many modern Eaton transmissions also feature a sight glass for quick fluid level checks during pre-trip inspections.

Service interval

The beauty of the Eaton PS-386 synthetic fluid is its longevity, but your service interval heavily depends on how the truck is used.

Normal Duty (Linehaul): For trucks strictly running over-the-road (OTR) on highways at steady speeds and standard weight limits, Eaton allows a massive interval of 500,000 miles. However, as a master tech, I recommend checking the fluid level and condition at every preventive maintenance (PM) A-service.

Severe Duty (Vocational / Towing): If your Peterbilt 579 is running in severe duty applications—such as heavy haul, logging, frequent stop-and-go city traffic, or operating in extremely dusty or mountainous environments—the fluid life drops significantly. In these conditions, you should perform a drain and fill every 180,000 miles or 3 years, whichever comes first.

Common transmission problems

While the Eaton Fuller Advantage and UltraShift AMTs in the 2016 Peterbilt 579 are generally bulletproof, they are not without their quirks.

• XY Shifter Failures: The XY shifter (the electronic actuator that shifts the gears on an AMT) is a common failure point. Symptoms include the truck refusing to go into gear or getting stuck in a particular gear. Often, this is preceded by fault codes on the dash.
• Wiring Harness Chafing: Heavy vibrations can cause the transmission wiring harness to chafe against the frame rails or transmission case. This leads to erratic shifting behavior, false sensor readings, or complete loss of communication with the Transmission Electronic Control Unit (TECU).
• Pneumatic Leaks: Eaton AMTs rely on the truck's air system to operate the clutch actuator. Air leaks in the transmission air lines, air filter regulator, or the clutch actuator itself can result in a truck that won't engage the clutch properly.
• Synchronizer Wear: In manual variants, drivers who "float" gears improperly can grind the synchronizers (in the auxiliary section) or the main box gears, leading to hard shifting or popping out of gear.

Transmission issues on Class 8 trucks require heavy-duty diagnostic software and serious tooling. If your rig is acting up, don't risk a breakdown on the interstate. Find a trusted shop on Repairius to keep your Peterbilt 579 shifting smoothly.