2015 Kenworth T680 Coolant Capacity & Type

The 2015 Kenworth T680 typically holds between 40 and 42 quarts (37.8 to 39.7 liters) of coolant in its cooling system.

Quick Answer

• Total Cooling System Capacity: 40-42 Quarts (37.8-39.7 Liters)
• OEM Coolant Spec: Extended Life Coolant (ELC) - Red/Pink or Purple, OAT (Organic Acid Technology) or HOAT (Hybrid Organic Acid Technology) depending on specific engine. Always refer to your engine manufacturer's specifications.
• Mix Ratio: 50/50 Pre-mix or 50% Concentrate with 50% distilled water.

Capacity by Engine Option

The Kenworth T680 was available with various engine options, primarily Cummins and PACCAR MX series engines. While the overall system capacity is similar, slight variations exist.

Always consult your owner's manual or engine service manual for the precise capacity for your specific engine configuration.

Flush Interval

Maintaining your coolant is crucial for the longevity of your engine and cooling system components.

• Normal Duty: For most long-haul operations under normal conditions, an ELC coolant typically has a service life of 600,000 miles, 12,000 hours, or 6 years, whichever comes first.
• Severe Duty: If your truck operates in severe conditions (e.g., extreme temperatures, excessive idling, frequent heavy loads, dusty environments), it's advisable to check your coolant condition more frequently and consider reducing the flush interval to 300,000 miles, 6,000 hours, or 3 years.

It is highly recommended to perform regular coolant analysis (every 100,000 miles or annually) to monitor the condition of your coolant and additives. This can help determine the optimal time for a flush and refill.

How to Refill & Bleed

Properly refilling and bleeding the cooling system after a drain or flush is critical to prevent air pockets, which can lead to overheating.

1. Drain the System: With the engine cool, open the drain valve on the bottom of the radiator and any drain plugs on the engine block. Allow all old coolant to drain completely.
2. Flush (Optional but Recommended): If performing a full flush, close drain valves and fill with distilled water and a reputable coolant system flush product. Run the engine to operating temperature with the heater on high, then drain again. Repeat with plain distilled water until the drained water is clear.
3. Close Drains: Close all radiator and engine block drain valves.
4. Fill with New Coolant: Slowly fill the degas bottle (coolant reservoir) with the specified 50/50 pre-mixed ELC. Filling slowly allows air to escape. Keep the heater control in the cab set to maximum heat to ensure the heater core fills.
5. Run Engine & Top Off: Start the engine and run it at idle with the reservoir cap off. As the engine warms up, the thermostat will open, and coolant will begin to circulate. Squeeze the upper and lower radiator hoses several times to help dislodge air bubbles.
6. Monitor Coolant Level: As the engine reaches operating temperature, the coolant level in the degas bottle will likely drop. Continue to add coolant to maintain the proper level (between the MIN and MAX marks).
7. Bleed Air: Many T680 models with Cummins and PACCAR engines are designed to self-bleed effectively. However, some systems may benefit from slightly revving the engine (to about 1200-1500 RPM) for a few minutes to encourage air to escape. Check for any dedicated bleed screws on the thermostat housing or other high points in the system, though these are less common on modern heavy-duty trucks which rely on the degas bottle.
8. Final Check: Once the engine is at operating temperature and the fan has cycled on and off a few times, install the reservoir cap. After a test drive and the engine has cooled completely, recheck the coolant level in the degas bottle and top off if necessary. Keep an eye on the coolant level for the next few days.

Common Cooling System Issues for this Generation

Owners of 2015 Kenworth T680 trucks may encounter various cooling system issues, some of which are common across heavy-duty trucks.

• Leaking Radiator or Hoses: Over time, vibrations and temperature cycles can cause leaks in the radiator core, radiator tanks, or hoses. Cracks in plastic end tanks are not uncommon.
• Thermostat Malfunctions: A stuck-open thermostat can lead to the engine running too cool, reducing fuel efficiency. A stuck-closed thermostat will cause rapid overheating.
• Water Pump Failure: The water pump