2018 Chevrolet Silverado 3500HD Coolant Capacity & Type

The 2018 Chevrolet Silverado 3500HD coolant capacity varies by engine, with the 6.0L V8 holding approximately 16.3 quarts (15.4 liters) and the 6.6L Duramax Diesel holding approximately 25.2 quarts (23.9 liters).

Quick answer

• Total Cooling System Capacity (approximate):
  • 6.0L V8: 16.3 quarts (15.4 liters)
  • 6.6L Duramax Diesel: 25.2 quarts (23.9 liters)
• OEM Coolant Spec: DEX-COOL (Orange/Red, HOAT/OAT blend, GM Dex-Cool approved)
• Mix Ratio: 50/50 pre-mix or 50/50 concentrate with distilled water

Capacity by engine option

Flush interval

Chevrolet recommends a coolant flush for the 2018 Silverado 3500HD every 5 years or 150,000 miles, whichever comes first, under normal driving conditions. For severe duty, such as frequent towing, extreme temperatures, or off-road use, it's wise to consider shortening this interval to every 3 years or 50,000-75,000 miles to ensure optimal cooling system performance and longevity.

How to refill & bleed

Refilling and bleeding a 2018 Chevrolet Silverado 3500HD cooling system correctly is crucial to prevent air pockets, which can lead to overheating. Always perform these steps on a cool engine.

1. Drain the System: Open the radiator drain cock (petcock) at the bottom of the radiator and remove the radiator cap to allow the old coolant to drain completely. For a more thorough drain, you may also need to open drain plugs on the engine block, referring to your service manual.
2. Flush (Optional but Recommended): After draining, close the drain cock and fill the system with distilled water. Run the engine with the heater on high until it reaches operating temperature. Drain the distilled water. Repeat this process until the drained water is clear, indicating a clean system. Do NOT use tap water for flushing or mixing, as minerals can cause deposits.
3. Refill with New Coolant: Close all drain points. Slowly pour a 50/50 mix of DEX-COOL approved coolant and distilled water into the radiator fill neck, or directly into the reservoir if the system is designed to be filled there (consult your owner's manual). Fill until the coolant level is at the "COLD FILL" line on the reservoir.
4. Bleed the System:
   • 6.0L V8: Start the engine with the radiator cap off (or reservoir cap off if it's the primary fill point) and the heater on high. As the engine warms up, air bubbles will escape. Continue to add coolant as needed to maintain the proper level. Squeeze the upper and lower radiator hoses gently several times to help dislodge air bubbles. Once the thermostat opens and coolant begins to circulate, you should see a steady flow. Install the radiator cap. Drive the vehicle, then recheck the coolant level in the reservoir once the engine has cooled down.
   • 6.6L Duramax Diesel: The Duramax system for this generation is generally self-bleeding, but it benefits from careful refilling. After filling, run the engine with the heater on high until operating temperature is reached. Monitor the coolant level in the reservoir and add as necessary. Some technicians may use a specialized vacuum filler to ensure no air is introduced into the system during the refill, which is highly recommended for diesel engines. There isn't typically a traditional "bleeder screw" on these systems; proper filling and running the engine with the caps off (if appropriate for the design) are key.
5. Final Check: After the engine has completely cooled, recheck the coolant level in the reservoir and top off if necessary. Keep an eye on the coolant level over the next few driving cycles.

Common cooling system issues

The 2018 Chevrolet Silverado 3500HD, particularly models from this generation, can experience a few common cooling system issues:

• Water Pump Failure: The water pump is a wear item, and signs of failure include leaks (often from a weep hole), grinding noises, or the engine overheating. This is more common with higher mileage.
• Thermostat Issues: A failing thermostat can cause the engine to overheat (stuck closed) or run too cool (stuck open), impacting performance and fuel economy. Check engine lights for thermostat-related codes are common.
• Radiator Leaks: Radiators can develop leaks over time due to corrosion, road debris, or stress on the plastic end tanks. Look for visible coolant stains or a drop in coolant level.
• Hose Leaks/Failures: Radiator hoses and heater hoses can degrade and crack, leading to leaks. Inspect hoses for cracks, bulges, or softness.
• Degraded DEX-COOL Coolant: If the DEX-COOL coolant is not flushed at the recommended intervals or if it's mixed with incompatible coolants, it can break down and become corrosive, leading to sludge formation and damage to various cooling system components, including the heater core and radiator.
• Coolant Reservoir Leaks/Cracks: The plastic coolant reservoir can develop cracks over time, leading to slow leaks and a loss of coolant.

Regular coolant system maintenance, including timely flushes with the correct DEX-COOL coolant, is key to preventing these issues.

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