2023 International LT Coolant Capacity & Type

The 2023 International LT holds approximately 40 to 56 quarts (37.8 to 53 liters or 10 to 14 gallons) of coolant, depending on the engine option, radiator size, and whether the truck is equipped with a sleeper cab heater core. As a Class 8 heavy-duty workhorse, maintaining the correct coolant level, chemistry, and cleanliness is critical for optimal engine performance and emissions system longevity.

Here is your comprehensive guide to the coolant requirements for the 2023 International LT.

Quick Answer

• Total Capacity: 40–56 quarts (10–14 gallons / 37.8–53 liters) depending on engine, frame, and HVAC options.
• OEM Coolant Spec: Heavy Duty Extended Life Coolant (ELC). Usually a Nitrite-Free Organic Acid Technology (OAT) coolant. Must meet Navistar CEMS B-1 Type III or Cummins CES 14603 specifications.
• Color: Typically Red or Yellow (depending on the exact ELC brand used at the factory or by the fleet).
• Mix Ratio: 50/50 mix of coolant and distilled/deionized water (or pre-mixed 50/50 ELC).

Capacity by Engine Option

The 2023 International LT is primarily offered with two heavy-duty engine options. Because coolant lines route through the chassis, radiator, and cab/sleeper HVAC systems, total capacity can vary. Always buy extra to account for system bleeding.

Note: Trucks with dual HVAC systems (large sleepers or APU tie-ins) will be on the higher end of these capacity ranges.

Flush Interval

Heavy-duty ELC is designed for the long haul, but it doesn't last forever. For the 2023 International LT using Nitrite-Free OAT ELC:

• Normal Duty / Highway: 600,000 miles, 12,000 engine hours, or 6 years (whichever comes first).
• Severe Duty / Vocational: 300,000 miles, 6,000 engine hours, or 3 years.
• Testing: It is highly recommended to use test strips every 50,000 miles or during routine PM services to check freeze point, pH levels, and carboxylate levels to ensure the additive package hasn't depleted.

How to Refill & Bleed

Air trapped in a heavy-duty cooling system can cause catastrophic damage, particularly to the EGR cooler and cylinder head.

1. Drain: Ensure the engine is completely cool. Remove the surge tank cap and open the petcock at the bottom of the radiator. Drain into large, environmentally safe drain pans.
2. Vacuum Fill (Recommended): Because of the complex routing through the EGR cooler and sleeper heater cores, using a pneumatic vacuum coolant filler is strongly recommended by both International and Cummins. This pulls a vacuum on the system, verifying there are no leaks, and then draws the 50/50 pre-mixed ELC into every void without creating air pockets.
3. Manual Fill & Bleed: If you must fill manually, pour coolant slowly into the surge tank. Open the specific bleeder valves (usually located near the EGR cooler or thermostat housing—refer to the engine service manual) until a steady stream of fluid escapes.
4. Warm Up: Start the engine and turn the cab and sleeper heaters to their maximum heat setting. Let the truck idle until it reaches operating temperature and the thermostat opens.
5. Top Off: Shut down the engine, let it cool, and check the surge tank. Top off to the "COLD MAX" line.

Common Cooling System Issues

While the 2023 International LT is relatively new, heavy-duty trucks share common cooling system stress points to watch for as the miles rack up:

• EGR Cooler Leaks: A primary failure point in modern diesels. If you are losing coolant but don't see external leaks, and the exhaust smells sweet or is throwing EGR codes, suspect the EGR cooler.
• Coolant Level Sensor Issues: The surge tank level sensor can become coated in sediment or fail electrically, causing a false "Low Coolant" warning or engine derate.
• Water Pump Weepage: Keep an eye on the weep hole on the water pump housing. While a tiny drop is normal during break-in, a steady drip indicates internal seal failure.
• Sleeper Heater Core Line Chafe: Long coolant lines routed under the cab to the sleeper can rub against the frame or brackets. Inspect these lines regularly for chafe marks.

Proper cooling system maintenance keeps your LT on the road and out of the bay. If you need professional diagnostics, a system flush, or EGR repairs, don't leave it to chance. Find a trusted shop on Repairius.