2018 International LT: Transmission Fluid & Service

Quick answer

• Transmission make/model: Eaton Endurant, Eaton Fuller Advantage, or Allison 3000/4000 series.
• OEM fluid spec: Eaton-approved PS-386 (Endurant), PS-164 rev 7 (Fuller Advantage), or Allison TES 295/TES 668 (Allison automatics).
• Drain & fill capacity: Varies from ~7.5 quarts (Endurant) to 16 quarts (Allison).
• Full overhaul capacity: Varies from ~9.5 quarts (Endurant) to 29 quarts (Allison).
• Filter OEM part number: Varies significantly by transmission model and chassis configuration. Verify with dealer or service manual.
• Recommended service interval: Up to 500,000–750,000 miles for linehaul applications with synthetic fluid, or much shorter intervals (e.g., 25,000–50,000 miles) for severe/vocational service.

Fluid type explained

The 2018 International LT was available with several different transmission options, primarily from Eaton and Allison. The most common are the Eaton Endurant automated manual, the Eaton Fuller Advantage series manual, and the Allison 3000/4000 series fully automatic transmissions. Each requires a specific fluid to ensure longevity and performance.

• Eaton Endurant: This advanced automated manual transmission is designed to use Eaton-approved PS-386 synthetic fluid. This is a "fill-for-life" fluid in many applications, designed for extreme thermal stability and shear resistance. Using a non-approved fluid can damage the sophisticated electronic shift actuators and lead to premature wear.
• Eaton Fuller Advantage: These manual transmissions typically specify Eaton Roadranger PS-164 rev 7 synthetic lubricant. It provides excellent wear protection for gears and bearings under heavy loads.
• Allison Automatics (3000/4000 RDS, etc.): Allison has long specified its own fluids. For this model year, look for an Allison TES 295 or the newer, backward-compatible TES 668 approved synthetic fluid. These fluids are critical for the health of the clutch packs, seals, and hydraulic controls within the torque converter and valve body.

Using a generic "universal" transmission fluid is not recommended. The additives, viscosity, and friction modifiers in these OEM-spec fluids are precisely engineered for each transmission's unique hardware and operating characteristics.

Service procedure

There are two primary methods for servicing a heavy-duty transmission: a "drain and fill" and a "full fluid exchange."

• Drain & Fill: This is the most common service. It involves draining the fluid from the transmission pan (and cooler, if equipped with a drain plug), replacing the filter(s), and refilling with fresh fluid. This method typically replaces 60-80% of the total fluid in the system. For an Eaton Endurant, this is around 7.5 quarts. For an Allison, it could be 16 quarts or more.
• Full Exchange: A full fluid exchange (or "flush") uses specialized equipment to pump out the old fluid from the pan, torque converter, and cooler lines while simultaneously refilling with new fluid. This method replaces nearly 100% of the fluid, which is beneficial if the old fluid is badly degraded or contaminated. However, it is more time-consuming and expensive. For an Allison 4000 series, a full overhaul can require up to 29 quarts of fluid.

For most routine services, a drain and fill that includes filter replacement is sufficient to replenish additives and maintain fluid quality.

Service interval

Service intervals for the 2018 International LT vary dramatically based on the transmission and how the truck is used.

• Normal Duty (Linehaul): Trucks operating in over-the-road, high-mileage applications can see extremely long service intervals when using the correct synthetic fluid.

  • Eaton Endurant (PS-386): Up to 750,000 miles for the initial factory fill.
  • Eaton Fuller Advantage (PS-164): Up to 500,000 miles.
  • Allison (TES 295/668): Often 150,000 miles or more, but depends heavily on the specific model and duty cycle. Regular fluid analysis is the best way to determine the ideal interval.

• Severe Duty / Vocational: Trucks used in construction, refuse, heavy towing, or frequent stop-and-go city driving put much more stress on the transmission and its fluid. Heat is the number one enemy of transmission fluid.

  • For these applications, intervals are drastically shortened. An initial service at 50,000 miles, with subsequent services every 25,000 to 50,000 miles (or annually), is common. For vocational Allison-equipped trucks, changing the fluid and filters every 25,000 miles is a safe benchmark.

Always consult the operator's manual or a certified technician to determine the correct interval for your specific application.

Common transmission problems

While generally reliable, each transmission has its own set of potential issues to watch for as miles accumulate.

• Eaton Endurant: Early models sometimes experienced issues with the shift controller logic or faulty position sensors, leading to "Fault to Neutral" events. Wiring harness chafing, particularly near the starter, could also cause communication errors between the TCM and the shifter. Most of these issues can be addressed with software updates or targeted wiring repairs.
• Eaton Fuller Manuals: These are legendary for their durability. Most problems are not with the core transmission but with external components like clutch linkage, input shaft seals, or air leaks in the range selector. A grinding shift is more often due to operator error or a clutch that isn't fully disengaging rather than an internal transmission fault.
• Allison Automatics: Sensor failures (speed sensors, in particular) are a common cause of shifting problems and check transmission lights. Overheating due to a clogged cooler or severe use can lead to slipping clutches and torque converter issues. Solenoid failures within the valve body can cause harsh shifts or the inability to engage certain gears.

Regular maintenance and using the correct OEM-specified fluid are the most effective ways to prevent these common problems and ensure your 2018 International LT remains a reliable workhorse.

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