2016 Kenworth T680 Coolant Capacity & Type

The 2016 Kenworth T680 holds approximately 44 to 56 quarts (11 to 14 gallons) of coolant, depending on the specific engine equipped and the size of the sleeper cab heating configuration. As an ASE-certified master technician, I know that maintaining the cooling system on a heavy-duty Class 8 truck like the T680 is absolutely critical for preventing catastrophic engine failure and minimizing costly downtime. Whether your rig is powered by a PACCAR or a Cummins engine, using the correct coolant chemistry is just as important as keeping the system full.

Quick answer

• Total cooling system capacity: Approximately 44.0 to 56.0 quarts (41.6 to 53.0 liters) / 11 to 14 gallons. Note that trucks with large sleepers and auxiliary bunk heaters will hold more than day cabs.
• OEM coolant spec: Heavy-Duty Extended Life Coolant (ELC). This is typically a Red/Magenta Nitrite-Free OAT (Organic Acid Technology) or NOAT (Nitrited Organic Acid Technology). PACCAR Genuine Extended Life Coolant or Cummins Fleetguard ES Compleat OAT (Red) are the standard manufacturer specifications.
• Mix ratio: 50/50 pre-mixed with distilled or deionized water. Do not use tap water in heavy-duty diesel cooling systems.

Capacity by engine option

The 2016 Kenworth T680 was primarily offered with two distinct heavy-duty diesel engines. Coolant capacities vary slightly based on the engine block and radiator package, as well as auxiliary cab heaters.

Note: Always verify the exact capacity in your owner's manual or service information software, as custom fleet specifications and auxiliary APUs can alter total system volume.

Flush interval

Heavy-duty Extended Life Coolant (ELC) is designed to go the distance, but it still degrades over time due to heat cycling and contamination.

• Normal Duty: For standard over-the-road highway hauling, the initial coolant flush interval is typically 600,000 miles, 12,000 operating hours, or 72 months (6 years), whichever comes first. Many ELCs require a coolant extender additive to be added at the 300,000-mile mark.
• Severe Duty: If the truck is used for heavy hauling, logging, frequent mountain grades, or experiences high idle times, check the coolant condition and inhibitor levels with test strips every preventative maintenance cycle. Flush the system at 400,000 miles or 4 years under these harsh conditions to protect the wet sleeve liners from cavitation.

How to refill & bleed

Because of the massive volume of coolant and the lengthy heater core lines running back to the sleeper cab, air pockets are a major concern when refilling a Kenworth T680.

1. Drain the system: Open the radiator petcock and remove the lower radiator hose if doing a full flush. Be sure to drain the engine block via the block drain plugs.
2. Use a Vacuum Fill Tool (Highly Recommended): For Class 8 trucks, a pneumatic vacuum coolant filler is the best way to ensure no air is trapped in the EGR cooler or sleeper heater lines. Pull a vacuum on the empty system, hold it to test for leaks, and allow the vacuum to siphon the 50/50 pre-mix into the system.
3. Manual Fill Method: If you do not have a vacuum filler, pour the coolant slowly into the surge tank to allow air to escape.
4. Bleed the system: Start the engine and turn the main cabin and sleeper cab heaters to their maximum heat settings. Let the engine idle up to operating temperature so the thermostats open.
5. Top off: Rev the engine slightly to push air through the lines. Shut the engine down, let it cool, and top off the surge tank to the "COLD MAX" line.

Common cooling system issues

For the 2016 Kenworth T680 generation, technicians frequently encounter a few specific cooling system ailments:

• EGR Cooler Leaks: Both the PACCAR MX-13 and Cummins ISX15 are known to occasionally suffer from internal EGR cooler failures. This allows coolant to leak into the exhaust system, causing mysterious coolant loss without external puddles, often accompanied by white exhaust smoke.
• Radiator Tank Seam Failures: The plastic end tanks on the aluminum radiators can develop stress cracks or gasket leaks where the plastic crimps to the aluminum core, especially after 400,000 miles of chassis twisting.
• Coolant Level Sensor Failures: The sensor in the surge tank can become coated in sludge or fail internally, causing a false "Low Coolant" warning and potential engine derating.
• Water Pump Weeping: Pay attention to the weep hole on the water pump. A slow drip indicates the internal shaft seal is failing and the pump requires replacement.

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