2020 Chevrolet Silverado 2500HD — Coolant Capacity & Type

The 2020 Chevrolet Silverado 2500HD holds between 16.4 and 30.6 quarts of coolant, depending on whether it is equipped with the 6.6L gasoline engine or the heavy-duty 6.6L Duramax turbo-diesel. As an ASE-certified master technician, I frequently service these heavy-duty workhorses, and maintaining the cooling system is absolutely critical to keeping that Allison transmission and heavy-duty powertrain operating at optimal temperatures, especially when towing heavy loads.

Below is your complete guide to the coolant capacity, type, and service procedures for the 2020 Chevy Silverado 2500HD.

Quick answer

Here is the essential cooling system information for your 2020 Silverado 2500HD:

• Total Cooling System Capacity: 16.4 quarts (15.5 liters) for the 6.6L Gas V8; up to 30.6 quarts (29.0 liters) for the 6.6L Duramax Diesel V8.
• OEM Coolant Spec: DEX-COOL® (Orange in color). This is an OAT (Organic Acid Technology) coolant meeting the GM spec GMW3420 (formerly GM 6277M).
• Mix Ratio: 50/50 mixture of DEX-COOL concentrate and clean, drinkable water (or distilled water). You can also purchase pre-mixed 50/50 DEX-COOL. Do not exceed a 70/30 mixture even in extreme cold.

Capacity by engine option

The 2020 model year brought a new 6.6L gasoline V8 to the 2500HD lineup, alongside the updated 6.6L Duramax diesel. Because the diesel requires massive cooling reserves for the engine, turbocharger, and emissions equipment, its capacity is nearly double that of the gas engine.

Note: Capacities are approximate and can vary slightly depending on optional equipment (such as auxiliary heater packages or PTO provisions). Always fill to the "Cold Fill" line on the surge tank.

Flush interval

GM recommends a specific maintenance schedule for the factory DEX-COOL coolant:

• Normal Duty: Drain, flush, and refill the cooling system every 150,000 miles or 5 years, whichever comes first.
• Severe Duty: If you are frequently towing heavy loads, idling for extended periods, or driving in extreme temperatures, it is highly recommended to inspect the coolant strength and level every 15,000 miles. Some fleet managers choose to flush the system at 100,000 miles to ensure peak corrosion protection for the engine block and heater core.

How to refill & bleed

Air pockets in the cooling system can cause localized overheating, which is especially dangerous for the turbocharger on the Duramax engine. Here is the best practice for refilling and bleeding:

1. Wait for the engine to cool entirely before opening the pressurized surge tank cap.
2. Drain the old coolant using the radiator petcock. Dispose of it properly at a recycling facility.
3. Use a Vacuum Fill Tool (Highly Recommended): For the 6.6L Duramax (and the 6.6L Gas), using a pneumatic vacuum coolant refill tool is the factory-preferred method. It pulls the cooling system into a deep vacuum, checking for leaks, and then draws the 50/50 DEX-COOL mixture into the block and heater core without introducing air.
4. Manual Bleed Procedure (If vacuum tool is unavailable): Fill the surge tank slowly to the cold fill line. Leave the cap off. Start the engine and turn the cabin heater to maximum heat and fan speed.
5. Let the engine idle until it reaches operating temperature (the upper radiator hose will become hot).
6. As the thermostat opens, the coolant level in the surge tank will drop. Top it off to the cold fill line.
7. Install the cap tightly, test drive the truck, and re-check the level the next morning when the engine is completely cold.

Common cooling system issues

While the 2020 Silverado 2500HD is a robust truck, there are a few cooling system quirks to watch out for as the mileage climbs:

• EGR Cooler Leaks (Duramax): The Exhaust Gas Recirculation (EGR) cooler on the L5P diesel can occasionally develop internal leaks over time. If you are slowly losing coolant but see no external leaks, the EGR cooler is a prime suspect.
• Water Pump Weep Hole: Keep an eye on the water pump weep hole. A small, dry crust of orange DEX-COOL is normal, but active dripping indicates the internal pump seal is failing and requires replacement.
• Mixing Coolants: The most common issue caused by owners is topping off the orange DEX-COOL with universal green or yellow coolants. This can cause the OAT chemistry to break down, leading to a sludgy buildup that clogs the heater core and radiator. Always stick to GM-approved DEX-COOL.

If you aren't comfortable tackling a massive 30-quart diesel coolant flush or vacuum-bleeding the system yourself, leave it to the pros. Find a trusted shop on Repairius.