2018 Isuzu NPR: Coolant Capacity & Type

The 2018 Isuzu NPR series holds between 15.1 and 29.8 quarts (14.3 to 28.2 liters) of coolant, depending on the engine option. Filling the cooling system correctly with the specified fluid is critical for the longevity of these workhorse trucks.

Quick Answer

• Total Cooling System Capacity:
  • 6.0L V8 Gas: 15.1 qts (14.3 L)
  • 5.2L I4 Diesel: 29.8 qts (28.2 L)
• OEM Coolant Specification: Isuzu Genuine Long-Life Antifreeze/Coolant (LLC). This is a red/pink, phosphate-enhanced Organic Acid Technology (P-OAT) coolant. It is critical to use a P-OAT formula and not a standard OAT (like Dex-Cool) or a Hybrid OAT (HOAT).
• Mix Ratio: 50/50 mix of coolant concentrate and distilled water. Pre-mixed 50/50 solutions are highly recommended to ensure the proper ratio and water quality.

Capacity by Engine Option

The 2018 NPR was available with two very different engines, each with its own cooling system and capacity. The diesel engine, with its extensive EGR cooling system, holds nearly double the coolant of the gasoline V8.

Flush Interval

Following the correct flush interval is key to preventing corrosion and component failure. Using the specified Isuzu P-OAT coolant is essential for achieving these long service intervals.

• Normal Duty: The factory-fill coolant is designed to last up to 120,000 miles (193,000 km) or 5 years for the initial service. Subsequent flushes are recommended every 75,000 miles (120,000 km) or 3-4 years.
• Severe Duty: For trucks used in heavy stop-and-go traffic, towing near maximum capacity, or operating in extreme temperatures, it is recommended to shorten the interval. A flush every 60,000 miles (96,000 km) provides a safe margin of protection.

How to Refill & Bleed

Airlocks are a common and serious issue on these trucks, especially the 5.2L diesel model, due to the complexity of the EGR and cabin heating circuits. An incomplete bleed can lead to overheating and engine damage.

1. Safety First: Ensure the engine is completely cool before opening the cooling system.
2. Drain: Open the radiator petcock to drain the radiator. There may be additional block drains on the engine.
3. Fill Slowly: Pour the 50/50 coolant mix into the degas bottle (surge tank) very slowly to allow air to escape as the system fills.
4. Bleed (5.2L Diesel): The 5.2L diesel engine has a bleed screw located on the thermostat housing or an adjacent coolant pipe. Open this screw during filling. When a steady stream of coolant emerges, close the bleeder. For best results, professional technicians strongly recommend using a vacuum-fill tool (such as an AirLift) to eliminate the risk of air pockets.
5. Run and Purge: Leave the degas bottle cap loose. Start the engine and turn the cabin heater on to the highest heat and fan speed. This circulates coolant through the heater core.
6. Top Off: As the engine warms up and the thermostat opens, the coolant level will drop. Continue to top off the degas bottle until the level remains stable. Bubbles may appear in the tank as air is purged.
7. Final Check: Once the engine is at full operating temperature and the cooling fans have cycled, shut it off and let it cool completely. Perform a final top-off of the coolant in the degas bottle to the "COLD" full line.

Common Cooling System Issues

• EGR Cooler Failure (5.2L Diesel): The EGR cooler is a known weak point. Internal leaks can cause unexplained coolant loss, white smoke from the exhaust (steam), and eventual overheating. This is often the most significant cooling system-related repair on the diesel models.
• Radiator Leaks: The radiators, which feature plastic end tanks crimped to an aluminum core, can develop leaks at the seams or from cracks in the plastic over time.
• Water Pump Failure: Like any vehicle, the water pump is a wear item. Signs of failure include a coolant leak from the weep hole on the bottom of the pump, a grinding noise from the pump bearing, or an overheating engine.
• Brittle Plastic Fittings (6.0L Gas): The GM 6.0L engine often uses plastic heater hose connectors that can become brittle with age and heat cycles, leading to sudden and significant coolant leaks.

Keeping your NPR's cooling system in top condition is essential for its reliability and your business. If you're experiencing any of these issues or are due for a coolant flush, find a trusted shop on Repairius.