2021 GMC Sierra 2500HD Coolant Capacity & Type

The 2021 GMC Sierra 2500HD's cooling system holds approximately 16.3-17.7 quarts (15.5-16.7 liters) of coolant, depending on the engine. This guide details everything you need to know about your truck's coolant.

Quick Answer

• Total Cooling System Capacity: 16.3-17.7 quarts (15.5-16.7 liters)
• OEM Coolant Spec: DEX-COOL (Orange/Reddish-Orange, OAT, GM Spec dex-cool)
• Mix Ratio: 50/50 Prediluted or 50/50 Concentrate/Distilled Water Mix

Capacity by Engine Option

Flush Interval

Maintaining your cooling system is crucial for the longevity of your 2021 GMC Sierra 2500HD. Adhere to the following flush intervals:

• Normal Duty: Replace DEX-COOL coolant every 5 years or 150,000 miles, whichever comes first.
• Severe Duty: If you frequently tow heavy loads, drive in extreme temperatures, or in dusty conditions, it's wise to inspect and potentially replace your coolant more frequently, possibly every 3 years or 45,000 miles.

How to Refill & Bleed

Refilling and bleeding the cooling system correctly is essential to prevent air pockets that can lead to overheating. For your 2021 GMC Sierra 2500HD, follow these general steps:

1. Safety First: Ensure the engine is completely cool before starting. Wear appropriate personal protective equipment (PPE), including gloves and eye protection.
2. Drain Old Coolant: Place a drain pan under the radiator drain plug (petcock). Open the plug and the radiator cap to allow the system to drain completely. For a full flush, you may need to run distilled water through the system after draining the old coolant.
3. Close Drain Plug: Once drained, securely close the radiator drain plug.
4. Refill with Correct Coolant: Slowly pour the specified DEX-COOL 50/50 mixture into the coolant reservoir until it reaches the FULL COLD line. For the Duramax engine, locate and open the bleed screws on the thermostat housing and possibly on hoses to aid in air release during the initial fill.
5. Bleed the System (Gasoline Engine): Start the engine with the heater on full blast (hot). Allow the engine to reach operating temperature, and the thermostat to open. As the engine warms up, the coolant level in the reservoir will likely drop as trapped air escapes. Continue to top off the reservoir to the FULL COLD line. Squeeze the upper and lower radiator hoses several times to help dislodge air bubbles.
6. Bleed the System (Diesel Engine): For the Duramax, opening the bleed screws during the initial fill is critical. After filling, start and run the engine with the heater on. Monitor the coolant level and top off as needed. You may need to repeatedly open and close the bleed screws until a steady stream of coolant (without air bubbles) emerges. Some technicians prefer using a vacuum fill tool to ensure all air is removed, especially with the Duramax.
7. Final Check: Once the engine is cool again, double-check the coolant level and top off if necessary. Monitor the coolant level over the next few drive cycles.

Common Cooling System Issues

While the 2021 GMC Sierra 2500HD is a robust truck, certain cooling system issues can arise, particularly as the vehicle ages or due to improper maintenance:

• Coolant Leaks: Common areas for leaks include the radiator, water pump, hoses, and coolant reservoir. DEX-COOL can sometimes be associated with internal gasket degradation if not maintained, leading to leaks.
• Water Pump Failure: The water pump is a critical component; signs of failure include leaks, screeching noises, or overheating.
• Thermostat Issues: A faulty thermostat can cause the engine to overheat (stuck closed) or run too cool (stuck open), impacting fuel efficiency and emissions.
• Radiator Clogs: Over time, sediment and debris can accumulate in the radiator, reducing its efficiency and leading to overheating. This is more prevalent if the coolant is not flushed at recommended intervals or if incorrect coolant types are mixed.
• Degradation of DEX-COOL: While a long-life coolant, DEX-COOL can degrade over time and become acidic, leading to corrosion and component failure if not replaced per manufacturer guidelines.

Regular inspection and adherence to the recommended maintenance schedule are key to preventing these issues.

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