2021 Peterbilt 579 — Coolant Capacity & Type

The 2021 Peterbilt 579 holds approximately 44 to 56 quarts (11 to 14 gallons / 41.6 to 53 liters) of coolant, heavily dependent on the specific engine option, sleeper size, and whether auxiliary bunk heaters are equipped. Heavy-duty trucks require precise cooling system maintenance to prevent catastrophic engine failure, especially considering the intense thermal loads from modern emissions systems like the EGR and SCR.

Quick answer

• Total cooling system capacity: 44 - 56 quarts (41.6 - 53 liters) depending on the engine and chassis configuration.
• OEM coolant spec: Heavy-Duty Extended Life Coolant (ELC). Modern PACCAR and Cummins engines require a Nitrite-Free OAT (Organic Acid Technology) coolant. This coolant is typically Red or Magenta in color and must meet ASTM D6210 standards (e.g., PACCAR Genuine Extended Life Coolant or Fleetguard ES Compleat OAT).
• Mix ratio: 50/50 pre-mixed with distilled or deionized water. Do not use tap water if mixing from concentrate, as heavy-duty systems are highly sensitive to mineral scale.

Capacity by engine option

Because the Peterbilt 579 is a Class 8 truck customizable for various applications, the coolant capacity varies primarily by the powerplant and radiator package. Note: Capacities are approximate and include standard heater core circuits.

Always verify your exact capacity by checking the surge tank levels during the bleeding process, as auxiliary APUs or bunk heaters will increase the total volume.

Flush interval

Heavy-duty Nitrite-Free OAT ELC is designed for the long haul, but it isn't completely maintenance-free.

• Normal Duty (Highway/Linehaul): Replace the coolant every 600,000 miles, 12,000 hours, or 4 to 6 years (whichever comes first). Coolant should be tested with test strips twice a year to verify freeze point and inhibitor levels.
• Severe Duty (Vocational/Heavy Haul): Replace the coolant every 300,000 miles or 6,000 hours. High engine loads and extreme operating conditions degrade OAT inhibitors more rapidly.

Unlike older IAT or hybrid coolants, Nitrite-Free OAT generally does not require Supplemental Coolant Additives (SCA) or mid-life extenders, provided the system is not diluted with unapproved coolants.

How to refill & bleed

Modern heavy-duty diesel engines, especially those with complex EGR coolers, are notoriously difficult to bleed manually. Air pockets trapped in the EGR cooler can cause the cooler to superheat and crack.

1. Drain the system: Open the radiator petcock and remove the lower radiator hose if a complete drain is necessary. Drain the block via the engine block drain plugs.
2. Use a Vacuum Fill Tool: For a 2021 Peterbilt 579, an OEM-approved vacuum cooling system filler (Airlift tool) is highly recommended. Apply vacuum to the surge tank to collapse the hoses and suck the 50/50 pre-mixed ELC directly into the system. This prevents 95% of airlocks.
3. Manual Bleed (If vacuum fill is unavailable): Fill the surge tank slowly. Open any specific engine air-bleed valves (often located near the thermostat housing or EGR cooler high-point).
4. Warm-up: Start the engine and turn the cab and sleeper bunk heaters to maximum heat.
5. High-Idle: Engage the cruise-control high-idle feature to bring the engine up to operating temperature so the thermostat opens.
6. Top Off: Once the thermostat opens and the system burps, the level in the surge tank will drop. Top it off to the "MAX COLD" line once the engine has completely cooled down.

Common cooling system issues

• EGR Cooler Leaks: While improved over older generations, the EGR coolers on both the MX-13 and X15 can still develop internal leaks if air pockets cause localized boiling. This usually presents as unexplained coolant loss with white exhaust smoke, rather than external dripping.
• Coolant Level Sensor Failures: The sensor in the Peterbilt surge tank is prone to false readings due to scale buildup or internal electrical faults, resulting in an erroneous "Low Coolant" dash warning and potential engine derate.
• Water Pump Weepage: The PACCAR MX engines occasionally experience premature water pump seal weeping. A small amount of dried red crust at the weep hole is normal, but active dripping requires pump replacement.
• Hose Clamp Tension: The constant-tension spring clamps on the large radiator hoses can lose their clamping force over hundreds of thousands of miles, leading to slow cold-weather leaks.

If you are dealing with an internal EGR leak, a failing water pump, or a persistent low coolant warning on your truck, do not risk a costly on-the-road breakdown. Find a trusted shop on Repairius.