2021 International LT Fluid Type Specs

Quick Reference

Fluid	Type/Spec	Capacity
Engine Oil	API CK-4; SAE 15W-40, 10W-30	44 quarts / 11 gallons (Cummins X15)
Engine Coolant	Extended Life Coolant (ELC) OAT; Cummins CES 14603	14.5 gallons / 55 liters
Transmission Fluid	SAE 50 (Manual); Eaton PS-386 (Automated Manual)	13-16 pints (Manual); 7.5 quarts (Automated Manual)
Rear Differential	API GL-5; SAE 75W-90, 80W-140	18-38 pints per axle
Brake Fluid	DOT 4	N/A (Air Brakes)
Power Steering Fluid	ATF Dexron III / Mercon	2-4 quarts
Windshield Washer Fluid	-30°F All-Season	1.5 gallons / 5.7 liters
Diesel Exhaust Fluid (DEF)	API Certified ISO 22241	10-23 gallons

Engine Oil

The 2021 International LT, most commonly equipped with the Cummins X15 engine, demands a high-quality diesel engine oil that meets the API CK-4 service category. This specification ensures the oil is formulated to protect against wear, deposits, and soot-induced thickening in modern, low-emission diesel engines. The most commonly recommended viscosity grades are SAE 15W-40 and 10W-30. SAE 15W-40 is the industry standard for on-highway diesel trucks, offering robust protection in a wide range of operating temperatures. SAE 10W-30 may be used to improve fuel economy and cold-start performance, but always verify its suitability for your specific engine and operating conditions in the owner's manual. Oil change intervals can be as high as 50,000 miles or more, depending on the duty cycle and oil analysis program. However, it is critical to adhere to the manufacturer's recommended intervals, especially when operating in severe service conditions.

Engine Coolant

Proper coolant maintenance is critical for the longevity of the Cummins X15 engine. The 2021 International LT uses an Organic Acid Technology (OAT) Extended Life Coolant (ELC). These coolants are typically red or orange and are formulated to provide protection for up to 600,000 miles or 12,000 hours. The correct specification to look for is Cummins CES 14603. It is crucial to never mix OAT coolants with conventional Inorganic Acid Technology (IAT) or Hybrid Organic Acid Technology (HOAT) coolants. Mixing coolant types can lead to a chemical reaction that gels the coolant, causing blockages in the radiator and heater core, leading to catastrophic engine overheating. If the coolant is ever low, top it off with a pre-mixed 50/50 OAT ELC that meets the Cummins specification.

Transmission Fluid

The type of transmission fluid required for a 2021 International LT depends on the transmission it is equipped with. For trucks with a manual transmission, a non-EP (Extreme Pressure) SAE 50 gear oil is the standard recommendation. For automated manual transmissions, such as the Eaton Endurant, a synthetic fluid meeting Eaton PS-386 specification is required. Using the wrong fluid in an automated manual transmission can cause shifting problems and premature wear. Always confirm the transmission type and consult the service manual for the exact fluid specification.

Rear Differential

The rear axles of the International LT require a gear oil that meets the API GL-5 service category. The viscosity grade will depend on the specific axle model and application, with SAE 75W-90 and 80W-140 being the most common. For axles equipped with a limited-slip differential, a friction modifier additive may be required. Always check the axle housing for a tag indicating the required fluid type and whether a friction modifier is needed. Using the incorrect gear oil can lead to excessive wear and potential failure of the differential.

Brake Fluid

The 2021 International LT is equipped with a full air brake system, which does not use traditional hydraulic brake fluid. The brake system operates on compressed air, so there is no brake fluid to check or change. However, it is essential to regularly drain the air tanks to remove any accumulated moisture, which can cause corrosion and other issues within the air brake system.

Power Steering Fluid

The power steering system in the 2021 International LT typically uses an automatic transmission fluid (ATF) that meets the Dexron III or Mercon specification. It is important to use a fluid that is specifically formulated for power steering systems, as using the wrong fluid can damage the pump and steering gear. Check the fluid level regularly and top it off as needed with the correct type of fluid.

Windshield Washer Fluid

For the windshield washer system, a quality all-season washer fluid with a freezing point of at least -30°F is recommended. This will ensure that the washer system is functional in all weather conditions. Do not use water alone, as it can freeze in the winter and does not have the cleaning power of a dedicated washer fluid.

Diesel Exhaust Fluid (DEF)

Like all modern diesel trucks, the 2021 International LT is equipped with a Selective Catalytic Reduction (SCR) system that requires Diesel Exhaust Fluid (DEF). DEF is a non-toxic solution of 32.5% urea and 67.5% de-ionized water. It is critical to use only DEF that is API certified and meets the ISO 22241 standard. Using contaminated or poor-quality DEF can damage the SCR system, leading to costly repairs and vehicle downtime. The DEF tank is typically located next to the fuel tank and has a blue cap.

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