2018 International LT Fluid Type, Spec, and Capacity Reference

Quick Reference: 2018 International LT Fluid Specs

Fluid	Type/Spec	Capacity
Engine Oil	API CK-4 or FA-4; SAE 15W-40, 10W-30, or 5W-40	44 quarts / 41.6 liters (Cummins X15)
Engine Coolant	Nitrite-Free Extended Life Coolant (OAT); Red/Orange	16.5 gallons / 62.5 liters (Cummins X15)
Transmission Fluid	Varies by transmission model (e.g., Eaton PS-386)	Varies greatly; check dipstick/fill plug
Rear Differential	API GL-5, SAE 75W-90, 80W-140, or 85W-140 Synthetic	Varies by axle model (approx. 20-40 pints)
Brake Fluid	Hydraulic Clutch System Only: DOT 3 or DOT 4	N/A (Air Brakes); Clutch: ~1 pint
Power Steering Fluid	Commercial Heavy-Duty Power Steering Fluid	Approx. 2-4 quarts
Windshield Washer Fluid	Standard Commercial Washer Fluid	Approx. 2.5 gallons / 9.5 liters
Diesel Exhaust Fluid (DEF)	API Certified ISO 22241	10-21 gallons / 38-80 liters

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Engine Oil

The 2018 International LT, most commonly equipped with the Cummins X15 engine, demands robust, high-performance diesel engine oil that meets the latest industry standards. The primary specification to look for is API Service Category CK-4 or FA-4.

• API CK-4: This oil is the direct successor to CJ-4 and is formulated for high-speed, four-stroke diesel engines designed to meet 2017 and later on-highway greenhouse gas (GHG) emission standards. It is backward-compatible, meaning it can be used in older engines that called for CJ-4, CI-4 Plus, etc.
• API FA-4: This is a lower-viscosity oil designed for select newer diesel engines to help maximize fuel economy. It is not interchangeable or backward-compatible with CK-4 oils. Using FA-4 in an engine not specifically designed for it can lead to inadequate protection and premature wear. Always verify in your owner's manual if FA-4 is permitted.

Viscosity Grades:

• 15W-40: The industry standard and most common choice for all-around performance in a wide range of operating temperatures.
• 10W-30: A popular choice for improved fuel economy and better cold-start performance.
• 5W-40 Synthetic: Offers the best cold-weather starting protection and high-temperature stability. It is often used in trucks operating in extreme climates.

Oil Change Interval: Intervals can vary significantly based on duty cycle, idle time, and fuel consumption. Modern LTs use an oil life monitoring system, but a typical interval under normal highway use is between 25,000 and 50,000 miles. Severe duty applications will require more frequent changes. Always consult the OEM service information for the schedule that fits your specific operation.

Engine Coolant

Proper coolant is critical for thermal management and corrosion prevention. The 2018 LT uses a Nitrite-Free, Organic Acid Technology (OAT) Extended Life Coolant (ELC). This is typically red or orange in color.

Do not use conventional green coolants or older Hybrid OAT (HOAT) coolants. Mixing coolant types can cause them to gel, leading to blockages in the radiator, heater core, and oil cooler, which can cause catastrophic engine overheating and damage. Only use a coolant that is specified as a Nitrite-Free OAT ELC. The system should be drained, flushed, and refilled every 600,000 miles, 12,000 hours, or 6 years, but it's essential to test the freeze point and additive strength regularly.

Transmission Fluid

Fluid specifications for the 2018 International LT are entirely dependent on the transmission installed. International offered a wide range of Eaton Fuller and Allison automatic and automated manual transmissions. There is no "one-size-fits-all" fluid.

• Eaton Fuller (Manual / Automated): Most modern Eaton transmissions require a fluid meeting Eaton specification PS-386. This is a high-performance, heavy-duty synthetic lubricant. Using older PS-164 spec fluid is not recommended for newer transmissions.
• Allison (Automatic): Allison automatic transmissions will require a fluid meeting Allison TES-295 or the newer TES-668 specification. These are fully synthetic fluids designed for severe duty and extended drain intervals.

Crucial Pitfall: Never use generic "universal" ATF or gear oil in these expensive and complex transmissions. Always identify the transmission model (usually via a tag on the housing) and use the exact fluid specified by the manufacturer. Checking the fluid level is also model-specific, involving a dipstick or a fill plug on the side of the case.

Rear Differential Fluid

The rear axles require a high-quality, synthetic gear lubricant meeting API Service GL-5. The viscosity grade depends on the specific axle model and ambient operating temperatures.

• SAE 75W-90 Synthetic: A common choice for many applications, offering a balance of protection and efficiency.
• SAE 80W-140 or 85W-140 Synthetic: Specified for heavy-haul or extreme temperature applications where additional thermal stability is required.

Some axles, particularly those with limited-slip or locking features, may require a specific friction modifier additive. Always consult the axle manufacturer's service manual (e.g., Meritor, Dana) to confirm the correct viscosity and any additive requirements.

Brake & Clutch Fluid

The primary service brakes on a 2018 International LT are air-operated, meaning they do not use brake fluid. The air system has its own maintenance requirements, including regularly draining the air tanks to remove moisture and servicing the air dryer cartridge.

However, if the truck is equipped with a manual transmission, the hydraulic clutch system uses standard automotive brake fluid. Use a high-quality DOT 3 or DOT 4 fluid from a sealed container. Do not use DOT 5 silicone fluid, as it is not compatible with the system's seals.

Power Steering Fluid

Use a high-quality commercial Heavy-Duty Power Steering Fluid. Do not substitute with automatic transmission fluid (ATF) unless it is explicitly permitted by the steering gear manufacturer. Using the wrong fluid can damage seals and compromise steering performance. The system capacity is relatively small, so check the level frequently.

Windshield Washer Fluid

Use any standard commercial-grade windshield washer solvent. For winter operation, ensure the fluid has an adequate anti-freeze rating to prevent the reservoir and lines from freezing and cracking.

Diesel Exhaust Fluid (DEF)

For the Selective Catalytic Reduction (SCR) system to function, the 2018 LT requires Diesel Exhaust Fluid (DEF). This fluid must be API certified and meet ISO 22241 specifications. Using non-compliant fluid can damage expensive SCR system components.

DEF is a solution of 32.5% urea in 67.5% de-ionized water. It is non-toxic but can be corrosive to certain materials. Always use dedicated, clean funnels and containers for handling DEF to avoid contamination, which can trigger fault codes and engine derating. Tank sizes vary by truck configuration, offering different ranges between fill-ups.

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