2025 International LT Fluid Specifications: Complete Mechanic's Guide

As an ASE-certified master technician who spends a lot of time around heavy-duty commercial fleets, I know that keeping a Class 8 workhorse like the 2025 International LT on the road comes down to one critical practice: strict adherence to factory-specified fluids and preventative maintenance schedules. Whether your LT is spec’d with the International S13 Integrated Powertrain or the venerable Cummins X15, pouring the wrong specification of fluid into these advanced systems can result in catastrophic downtime and voided warranties.

Below is your complete, master-tech guide to the exact fluid types, specifications, and capacities for the 2025 International LT.

Quick reference

Note: Capacities vary significantly based on exact chassis spec, engine choice (S13 vs. Cummins X15), oil pan size, transmission configuration, and axle manufacturer (Dana vs. Meritor). Always verify exact volumes in your owner’s manual or OEM service info.

Fluid	Type/Spec	Capacity
Engine Oil (Cummins X15)	API CK-4 or FA-4, 10W-30 or 5W-40 (Cummins CES 20086 / 20087)	Approx. 11-12 Gal (42-45 L)
Engine Oil (Intl S13)	API FA-4, 5W-30 (Navistar approved)	Approx. 11 Gal (42 L)
Engine Coolant	Nitrite-Free OAT ELC (Navistar CEMS B-1 Type III / Cummins CES 14603)	12-15 Gal (System dependent)
Transmission (T14 / Eaton)	Synthetic PS-386 (Eaton/Navistar approved)	16-18 Pints (verify by model)
Drive Axles (Differentials)	Full Synthetic 75W-90 or 80W-140 (API GL-5, SAE J2360)	30-40 Pints per axle
Brake Fluid	N/A (Air Brake System) - Air Dryer Cartridge Maintenance	N/A
Power Steering	Dexron III / Mercon equivalent or Navistar Spec	3-4 Quarts
Diesel Exhaust Fluid (DEF)	API Certified to ISO 22241 standard	15-23 Gal (Tank dependent)
Windshield Washer Fluid	Standard all-season washer fluid	1-2 Gallons

Engine Oil

Modern commercial diesels are highly sensitive to oil specifications due to complex emissions systems (DPF/SCR) and tight bearing tolerances.

• Specification: For the Cummins X15, you must use an oil meeting Cummins CES 20086 (API CK-4) or CES 20087 (API FA-4). For the International S13 powertrain, low-viscosity API FA-4 (5W-30) is typically factory fill to maximize fuel economy.
• Intervals: Depending on duty cycle, idle time, and fuel economy, intervals can range from 30,000 miles up to 75,000 miles (with oil sampling).
• Pitfall: Never substitute legacy API CJ-4 oils in these engines, as the ash content can rapidly plug the Diesel Particulate Filter (DPF). Furthermore, do not mix CK-4 and FA-4 oils; FA-4 is a lower high-temperature high-shear (HTHS) viscosity oil specifically engineered for modern efficiency.

Engine Coolant

The cooling system is the lifeblood of heavy-duty emissions control systems and EGR coolers.

• Specification: The 2025 LT uses a Nitrite-Free Extended Life Coolant (NF-OAT ELC), typically red/magenta in color. Look for Navistar CEMS B-1 Type III or Cummins CES 14603 approvals.
• Intervals: Typically rated for 600,000 miles or 12,000 hours, often requiring an extender at half-life.
• Pitfall: Do not mix OAT coolant with old-school conventional green coolant or HOAT (Hybrid OAT) fluids containing nitrites or silicates. Mixing coolant types will cause additive drop-out, leading to sludge formation, water pump failure, and catastrophic EGR cooler failure.

Transmission Fluid

Whether your LT is equipped with the International T14 automated manual transmission (AMT) or an Eaton Endurant AMT, proper lubrication is required for the pneumatic shifting actuators and internal gearing.

• Specification: Approved full synthetic transmission fluid meeting the PS-386 specification (e.g., Eaton PS-386).
• Intervals: Synthetic fluids in modern AMTs typically boast service intervals of up to 500,000 miles in line-haul applications.
• Pitfall: Never use universal ATF, standard gear lube, or older PS-164 rev 7 fluids in these modern AMTs. Using the wrong viscosity will cause shifting delays, actuator failure, and gear grinding.

Drive Axles (Front and Rear Differentials)

The heavy-duty tandem rear axles (typically Dana or Meritor) require robust extreme-pressure protection.

• Specification: Full synthetic gear lubricant meeting API GL-5 and SAE J2360 standards. Viscosity is typically 75W-90 for standard climates or 80W-140 for extreme heavy hauling or hot climates.
• Intervals: Factory fill synthetics usually last 500,000 miles in on-highway line-haul duty. Severe duty drops this to 250,000 miles or less.
• Pitfall: Overfilling the axles can cause foaming and push fluid out of the axle seals. Always fill only to the bottom of the fill plug threads.

Brake System

• Specification: The 2025 International LT is a Class 8 truck equipped with an Air Brake System, meaning there is no hydraulic brake fluid (DOT 3/4) on board.
• Maintenance Note: Instead of flushing brake fluid, your maintenance focus must be on the air dryer desiccant cartridge. Replace the coalescing air dryer filter annually (before winter) to prevent moisture and oil blow-by from freezing in the air lines and destroying expensive brake valves.

Power Steering

• Specification: Heavy-duty power steering systems typically utilize automatic transmission fluid such as Dexron III / Mercon or a heavy-duty specific power steering fluid approved by Navistar.
• Intervals: Check at every PM. Flush and replace the fluid and the internal power steering reservoir filter every 100,000 miles.
• Pitfall: Neglecting to change the power steering filter inside the reservoir will starve the gear-driven steering pump, leading to pump cavitation and failure.

Diesel Exhaust Fluid (DEF)

• Specification: Must meet the ISO 22241 standard.
• Pitfall: DEF is highly susceptible to contamination. Never use funnels that have touched oil, coolant, or fuel. Even a microscopic drop of petroleum will destroy the DEF header sensors and the SCR catalyst, resulting in a derate condition and thousands of dollars in repairs. Keep the DEF cap clean.

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