2019 GMC Sierra 2500HD Coolant Capacity & Type Guide

The 2019 GMC Sierra 2500HD holds between 17.4 quarts (16.5 liters) and 29.4 quarts (27.8 liters) of coolant, depending entirely on which engine is under the hood. As an ASE-certified master technician, I frequently service heavy-duty trucks like the Sierra 2500HD, and maintaining the complex cooling systems on these workhorses is critical. Whether you are towing heavy loads with the Duramax diesel or using the 6.0L gas engine for daily contracting work, keeping your cooling system filled with the correct fluid is the key to preventing catastrophic engine failure.

Below is your comprehensive guide to the coolant capacity, specifications, and maintenance procedures for the 2019 GMC Sierra 2500HD.

Quick answer

When servicing the cooling system on your 2019 Sierra 2500HD, keep these primary specifications in mind:

• Total cooling system capacity: 17.4 quarts (16.5 L) for the 6.0L V8 Gas; 29.4 quarts (27.8 L) for the 6.6L V8 Duramax Diesel.
• OEM coolant spec: AC Delco DEX-COOL. This is an Orange, OAT (Organic Acid Technology) coolant meeting the GM 6277M and GMW3420 specifications.
• Mix ratio: A 50/50 mixture of DEX-COOL concentrate and clean, distilled water is required. You can also purchase pre-mixed 50/50 DEX-COOL. In extreme cold climates (below -34°F), a 60/40 coolant-to-water ratio may be used, but never exceed 70% coolant.

Capacity by engine option

Because the thermal demands of a high-output turbo-diesel are vastly different from a naturally aspirated gas V8, the fluid capacities reflect those differences. The Duramax features a massive primary cooling system to handle extreme towing temperatures.

Note: Capacities are approximate and include the engine block, radiator, heater core, and expansion tank. Always verify fluid levels via the surge tank cold-fill lines after a complete bleed.

Flush interval

General Motors uses DEX-COOL for its long-life properties, but it is not a lifetime fluid.

• Normal Duty: Replace the coolant every 5 years or 150,000 miles, whichever comes first.
• Severe Duty: If you frequently tow heavy trailers, idle for extended periods, or operate in extreme heat or dusty environments, it is highly recommended to flush the cooling system every 75,000 to 100,000 miles.

Leaving DEX-COOL in the system beyond its lifespan can cause the OAT additives to break down, leading to sludge formation and internal corrosion.

How to refill & bleed

The 2019 Sierra 2500HD requires a specific bleeding procedure to ensure all air is evacuated from the engine block and heater core. Air pockets can cause localized boiling and severe engine damage.

1. Drain the system: With the engine cold, open the radiator petcock. For a full flush, remove the lower radiator hose and engine block drain plugs.
2. Vacuum fill (Recommended): Because of the size and complexity of these cooling systems (especially the 6.6L Duramax), using a pneumatic vacuum coolant filler tool is the best way to refill. This tool pulls a vacuum on the entire system and sucks the new 50/50 coolant mixture in, preventing air pockets.
3. Manual refill & bleed (Alternative): If you don't have a vacuum filler, slowly pour coolant into the surge tank until it reaches the cold fill line. On the 6.6L Duramax, locate the bleeder screw near the thermostat housing and open it until a steady stream of fluid escapes, then tighten it.
4. Warm-up: Start the engine and turn the cabin heater to maximum heat and blower speed. Allow the engine to idle until it reaches operating temperature and the upper radiator hose gets hot (indicating the thermostat has opened).
5. Top off: Shut off the engine, let it cool completely, and check the surge tank. Top off to the "Cold Fill" line as necessary. Repeat this check after your first few drives.

Common cooling system issues

For the 2019 generation of the Sierra 2500HD, keep an eye out for these known cooling system weaknesses:

• Duramax Water Pump Leaks: The L5P 6.6L Duramax water pumps are known to develop weeping leaks at the weep hole as the internal seals age. If you smell sweet coolant but don't see a puddle, inspect the water pump housing.
• Radiator End Tank Separation: Like many modern vehicles, the Sierra utilizes an aluminum radiator with crimped plastic end tanks. Constant thermal cycling can cause the plastic tanks to crack or the crimp seals to fail, resulting in slow leaks.
• DEX-COOL Sludging: If a previous owner mixed standard green IAT (Inorganic Additive Technology) coolant or universal fluids with the factory DEX-COOL, a chemical reaction occurs that turns the coolant into a thick, abrasive gel. This restricts the heater core and radiator passages, necessitating a massive chemical flush.

Taking care of your heavy-duty truck's cooling system is the best way to ensure it stays on the road and out of the shop. If you suspect a leak or need a professional vacuum-flush service, find a trusted shop on Repairius.