2024 GMC Sierra 2500HD — Coolant Capacity & Type

The 2024 GMC Sierra 2500HD holds between 17.4 quarts and 29.5 quarts (16.5 to 27.9 liters) of coolant, depending on whether it is equipped with the 6.6L Gas V8 or the 6.6L Duramax Turbo-Diesel V8 engine.

As an ASE-certified master technician, I regularly service these heavy-duty trucks. Proper cooling system maintenance is critical, particularly if you are using your Sierra to tow heavy loads or haul significant payloads. Below is the essential information you need to maintain the cooling system on your 2024 GMC Sierra 2500HD.

Quick answer

• Total cooling system capacity: 17.4 quarts (16.5 L) for gas engines, up to 29.5 quarts (27.9 L) for diesel engines.
• OEM coolant spec: ACDelco DEX-COOL® (Orange). This is an OAT (Organic Acid Technology) coolant meeting GM specification GMW3420.
• Mix ratio: 50/50 mixture of DEX-COOL concentrate and clean, drinkable water (preferably distilled or deionized). Do not use a heavier concentrate unless operating in extreme sub-zero conditions (up to 60/40 maximum).

Capacity by engine option

The 2024 Sierra 2500HD comes with two distinct engine options, both requiring substantial amounts of coolant due to their heavy-duty applications.

Note: The Duramax diesel engine has a highly complex cooling system that supports not just the engine block, but also the turbocharger, EGR system, and transmission cooler. Capacities are approximate and can vary slightly based on specific cab/bed/options configurations.

Flush interval

General Motors specifies a long-life maintenance schedule for DEX-COOL, provided the system is never contaminated with non-OAT coolants.

• Normal Duty: Replace the engine coolant every 150,000 miles or 5 years, 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 inspect the coolant at 75,000 miles and consider flushing it by 100,000 miles or 4 years.

How to refill & bleed

Because of the massive capacity and complex routing of the 2024 Sierra 2500HD cooling system—especially on the Duramax—air pockets can be notoriously difficult to remove using traditional methods.

1. Drain the system: Wait until the engine is completely cool. Open the radiator drain petcock and allow the old coolant to empty into a large catch pan.
2. Vacuum Fill (Recommended): I highly recommend using a pneumatic vacuum coolant filler (like an Airlift tool) attached to the surge tank. This draws a vacuum on the entire system, preventing airlocks in the heater core or EGR cooler, and pulls the new 50/50 DEX-COOL mix in perfectly.
3. Manual Bleed (If vacuum fill is unavailable): Slowly fill the surge tank to the "Cold Fill" line. Leave the cap off.
4. Run the engine: Start the truck and turn the cabin heater to the maximum heat setting and the fan on low.
5. Bleed out air: Allow the engine to idle until it reaches operating temperature and the thermostat opens (the upper radiator hose will become hot). Watch the surge tank and add coolant as the level drops.
6. Final top-off: Once the level stabilizes, install the surge tank cap. Drive the vehicle, let it cool down completely, and recheck the level, topping off to the "Cold Fill" mark as necessary.

Common cooling system issues

While the 2024 Sierra 2500HD is a robust truck, there are a few cooling system quirks you should keep an eye on as the miles rack up:

• Duramax EGR Cooler Leaks: On diesel models, internal leaks in the EGR cooler can cause coolant loss without leaving a visible puddle under the truck. If you are constantly topping off your surge tank but see no external leaks, have the EGR system pressure tested.
• Surge Tank Cracks: The pressurized plastic coolant surge tanks are subjected to extreme under-hood temperatures. Over time (usually past the 5-year mark), the plastic can become brittle and develop hairline cracks along the seams.
• Water Pump Weepage: High mileage and heavy towing can wear out the water pump bearings and seals. A slow drip from the water pump weep hole is a sign that replacement is imminent.
• Thermostat Failures: Dual thermostats are used on the Duramax to manage massive thermal loads. If they stick open, you'll experience poor heater performance and a check engine light for engine under-temperature (P0128).

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