2018 Chevrolet Silverado 2500HD — Coolant Capacity & Type

The 2018 Chevrolet Silverado 2500HD holds between 16.7 quarts and 31.4 quarts of coolant, depending on whether it is equipped with the 6.0L gasoline engine or the 6.6L Duramax diesel. As an ASE-certified master technician, I regularly service these heavy-duty trucks, and keeping the cooling system in top shape is absolutely critical, especially if you use your 2500HD for heavy towing or hauling.

Quick answer

Here are the essential cooling system specifications for the 2018 Chevy Silverado 2500HD:

• Total cooling system capacity: 16.7 to 31.4 quarts (15.8 to 29.7 liters) depending on the engine.
• OEM coolant spec: DEX-COOL. This is an Orange, OAT (Organic Acid Technology) coolant meeting the GM 6277M specification.
• Mix ratio: A 50/50 mix of DEX-COOL concentrate and distilled water, or a 50/50 pre-mixed solution. Do not use tap water, as the minerals will degrade the cooling system components.

Capacity by engine option

The engine under the hood drastically changes how much coolant your truck requires. The Duramax diesel has a massive cooling system to handle the extreme heat of towing and turbocharging.

Note: Capacities are approximate. If you have auxiliary heating or cooling options, your capacity may be slightly higher.

Flush interval

General Motors uses extended-life coolant in these trucks, but it doesn't last forever. The OAT corrosion inhibitors eventually break down.

• Normal Duty: GM recommends flushing the cooling system every 150,000 miles or 5 years, whichever comes first.
• Severe Duty: If you frequently tow heavy loads, idle extensively, or operate in extreme heat or dusty environments, it is highly recommended to inspect the coolant strength every 30,000 miles and consider flushing it closer to the 100,000-mile or 4-year mark.

How to refill & bleed

Bleeding the air out of a modern heavy-duty cooling system can be tricky, especially on the 6.6L L5P Duramax. Air pockets can cause severe localized overheating and heater core issues.

1. Drain the system: With the engine cold, open the radiator drain petcock. Dispose of the old DEX-COOL properly.
2. Vacuum fill (Highly Recommended): For both the 6.0L and the 6.6L, using a pneumatic vacuum coolant filler is the professional standard. This tool draws the cooling system into a deep vacuum, testing for leaks, and then sucks the new 50/50 coolant mix into every void, eliminating air pockets instantly.
3. Manual fill (If no vacuum tool is available): Slowly pour the 50/50 DEX-COOL mixture into the surge tank until it reaches the cold fill line.
4. Bleed: Start the engine with the surge tank cap off. Let it idle and reach operating temperature so the thermostat opens. Turn the cabin heater to maximum heat and fan speed to ensure coolant flows through the heater core.
5. Top off: As the system burps out air, the level in the surge tank will drop. Add coolant as necessary. Once the level stabilizes and you have hot air coming from the cabin vents, install the cap. Recheck the level after your first long drive (once it cools down).

Common cooling system issues

For the 2018 Silverado 2500HD generation, there are a few common issues we see in the shop:

• Radiator End Tank Leaks: The crimped connection where the plastic end tanks meet the aluminum radiator core is prone to seeping over time, especially after years of chassis flex and thermal expansion. You will typically spot orange crust on the sides of the radiator.
• Duramax Water Pump Failures: While the L5P engine is very robust, the water pumps can eventually develop weep hole leaks or bearing play. If you smell sweet coolant but can't find a leak up top, check around the water pump pulley.
• Coolant Contamination (Sludging): DEX-COOL is heavily reliant on remaining uncontaminated. If someone previously topped off your truck with a conventional green IAT coolant or universal "all makes/all models" coolant, it can react with the DEX-COOL and form a thick, brown sludge that clogs the heater core and radiator.

Proper maintenance will keep your Silverado running cool, whether it's empty or hauling a fifth-wheel trailer. If you need a professional to handle your flush or diagnose a leak, find a trusted shop on Repairius.