Duramax Coolant Type and Capacity by Generation

Every generation of the Duramax diesel, from the original LB7 through the current L5P, was designed around GM's orange Dex-Cool coolant. The chemistry has stayed consistent, but capacities and service details vary by truck. This guide gives you the general picture; refer to your owner's manual for the exact figures for your year and configuration.

Coolant type across the generations

All Duramax generations use an orange organic-acid (OAT) coolant, commonly known as Dex-Cool.

• LB7, LLY, LBZ, LMM, LML, L5P: orange Dex-Cool OAT is the factory fill for the platform.
• Do not mix chemistries: mixing Dex-Cool with green or other coolants degrades protection and can cause deposits.
• Use distilled water: if mixing concentrate, use distilled water to avoid mineral scale.

Typical system capacity

• Full system: generally around 6 gallons across the generations, varying by cab, radiator and configuration.
• Newer trucks: the L5P and later emissions-equipped trucks may have additional cooling circuits; refer to your manual.
• Always verify: fill to the cold line and recheck after the engine has cycled and burped air.

Service intervals

• Flush interval: extended-life Dex-Cool typically runs a long interval, often several years or around 100,000 to 150,000 miles; refer to your manual.
• Condition checks: inspect coolant color and level at every oil change; rusty or muddy coolant means service is overdue.
• Inspect hardware: water pump, thermostat, radiator and hoses at flush time. The water pump is a known wear item on the Duramax.

Glow plugs, not a grid heater

Unlike a Cummins, the Duramax uses glow plugs for cold starting, managed by a glow plug control module. Keep this in mind when comparing platforms, and diagnose the module before condemning the plugs if cold starts get rough.

Need a correct water pump, thermostat, or radiator for your Duramax generation? Email sales@coredieselparts.com with your VIN and we will match the right part.

Frequently asked questions

Do all Duramax engines use the same coolant?

They all use orange Dex-Cool OAT coolant, though capacities and cooling-circuit details differ by generation. Refer to your manual for the exact specification and capacity for your truck.

Can I switch my Duramax to green coolant?

The platform is designed for Dex-Cool. Switching chemistries requires a complete flush and is generally not recommended. Staying on the correct OAT coolant avoids compatibility problems.

How do I know if my Duramax coolant needs replacing?

Check color and clarity. Bright orange and clean is good; muddy, brown, or rusty coolant, or coolant past its service interval, should be flushed and replaced. Inspect the water pump at the same time.