2015 GMC Sierra 2500HD – Coolant Capacity & Type

The 2015 GMC Sierra 2500HD holds approximately 18.7 quarts (17.7 liters) of coolant with the 6.0L LY6/L96 V8 engine, and approximately 25.2 quarts (23.9 liters) with the 6.6L LML Duramax Diesel engine. This measurement includes the coolant found in the radiator, engine block, and heater core.

Quick Answer

• Total Cooling System Capacity (6.0L Gasoline): 18.7 quarts (17.7 liters)
• Total Cooling System Capacity (6.6L Duramax Diesel): 25.2 quarts (23.9 liters)
• OEM Coolant Spec: DEX-COOL (Orange/Reddish-Orange, OAT, GM Spec GMW3420 or GM6277M)
• Mix Ratio: 50/50 Pre-mix (or 50% concentrate / 50% distilled water)

Capacity by Engine Option

Flush Interval

Maintaining your coolant is crucial for the longevity of your 2015 GMC Sierra 2500HD's engine. Adhere to the following flush intervals:

• Normal Duty: Replace every 5 years or 150,000 miles, whichever comes first.
• Severe Duty: If your truck sees heavy towing, frequent off-road use, or operates in extreme temperatures, it's wise to consider flushing and replacing the coolant every 3 years or 45,000 miles.

How to Refill & Bleed

Properly refilling and bleeding the cooling system after a flush or repair is critical to prevent air pockets, which can lead to overheating. Always perform this on a cool engine.

1. Drain the System: Open the radiator drain cock and remove the radiator cap. Ensure the heater is set to full hot to allow coolant to drain from the heater core. For a full flush, disconnect the lower radiator hose.
2. Rinse (Optional but Recommended): If performing a full flush, you can run distilled water through the system until it runs clear. Avoid using tap water for this.
3. Close Drain & Reconnect Hoses: Securely close the radiator drain cock and reattach any disconnected hoses.
4. Fill with Correct Coolant: Slowly fill the degas bottle (coolant reservoir) with the specified DEX-COOL 50/50 mixture. Fill to the "COLD FILL" line.
5. Bleeding (6.0L Gasoline): Start the engine with the heater on high and the fan on low. Allow the engine to reach operating temperature. As the engine warms up, the thermostat will open, and the coolant level in the degas bottle may drop. Add more coolant as needed to maintain the "COLD FILL" line. Briefly rev the engine to 2,000-2,500 RPM a few times. Some 6.0L engines may have a bleeder screw near the thermostat housing; open it until a steady stream of coolant (without air bubbles) appears, then close it.
6. Bleeding (6.6L Duramax Diesel): The Duramax system is largely self-bleeding through the degas bottle. Fill to the "COLD FILL" line. Start the engine and run with the heater on high. The system will purge air through the degas bottle. Monitor the level and top off as necessary. Some technicians prefer to slightly elevate the front of the vehicle to aid in air removal. There may be a bleed screw on the thermostat housing (typically an 8mm or 10mm hex head); open it carefully until coolant flows out to ensure air is purged from the highest points.
7. Drive Cycle & Recheck: Drive the vehicle through at least one full warm-up and cool-down cycle. After the engine has completely cooled, recheck the coolant level in the degas bottle and top off if necessary. Repeat this check over the next few days.

Common Cooling System Issues for this Generation

Owners of 2015 GMC Sierra 2500HD trucks may encounter specific cooling system issues related to this generation:

• Water Pump Failure: The 6.0L gasoline engines, in particular, are known for water pump failures, often indicated by a coolant leak from the weep hole or a grinding noise. The 6.6L Duramax diesel engine can also experience water pump issues, although less frequently.
• Radiator Leaks: Over time, the plastic end tanks on the radiators can become brittle and crack, leading to coolant leaks. Corrosion within the radiator core can also be a source of leaks.
• Thermostat Issues: A failing thermostat can cause the engine to overheat or run too cool. Symptoms include fluctuating temperature gauges, slow warm-up, or the engine overheating in traffic.
• Degas Bottle/Reservoir Cracks: The plastic coolant reservoir can develop hairline cracks, leading to slow coolant loss that can be difficult to diagnose. Inspect the bottle regularly for any signs of cracking or discoloration.
• Hose Leaks/Wear: Radiator hoses and heater hoses can degrade over time, leading to leaks. Inspect hoses for swelling, cracks, or softness.
• EGR Cooler Issues (6.6L Duramax): On the Duramax diesel, issues with the Exhaust Gas Recirculation (EGR) cooler can lead to coolant loss internally, sometimes without external leaks. Symptoms might include white smoke from the exhaust or coolant consumption.

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