2019 Kenworth T680 — Coolant Capacity & Type

The 2019 Kenworth T680 holds roughly 11–16 gallons (44–64 quarts, ~42–61 liters) of coolant in total, depending on engine (PACCAR MX-11/MX-13 or Cummins X15), heater circuit length, and any add-on systems such as an APU.

Quick answer

• Total cooling system capacity: about 44–64 quarts (42–61 L)
• OEM coolant spec: Heavy‑duty Extended Life Coolant (ELC), OAT chemistry, typically red/magenta; use a product meeting ASTM D6210 and TMC RP 329/330. For Cummins X15, use a coolant meeting current Cummins requirements (e.g., CES 14603/Fleetguard ES standards); for PACCAR MX engines, use PACCAR‑approved OAT (nitrite‑free OAT is commonly specified).
• Mix ratio: 50/50 premix (or 50% concentrate + 50% deionized/distilled water). Do not exceed 60% antifreeze.

Capacity by engine option

Actual capacity varies with radiator size, cab/sleeper heater loop length, and accessories (APU, fuel‑fired heater), but these ranges are typical for a T680:

Note: APUs and auxiliary heaters can add ~0.5–1.5 gal (2–6 L) to the system.

Flush interval

• Normal service (ELC/OAT): typically 600,000 miles or 6 years (≈12,000 engine hours). Many ELCs allow extension to 1,000,000 miles with a mid‑life extender at ~300,000 miles—follow the coolant manufacturer’s directions.
• Severe duty (heavy idling, dusty/dirty coolers, frequent high‑load or mountain operation): 300,000 miles or 3 years, with more frequent checks of freeze point and inhibitor level.
• Conventional (IAT) coolant, if used: drain/flush about every 150,000 miles or 2 years and maintain SCA/DCA levels per TMC RP 329.

Always confirm intervals in the engine OEM manual for your exact coolant brand and chemistry.

How to refill & bleed

1. Preparation
   • Park level, set brake, allow engine to cool. Open the cab heater valves (set HVAC to full hot). Have new ELC/OAT 50/50 premix ready (or concentrate plus deionized water).
2. Drain
   • Open radiator drain and the engine block drains (many HD engines have at least one block drain). Catch and dispose of old coolant properly. If contaminated, perform a distilled‑water flush until clear.
3. Refill (vacuum‑fill preferred)
   • Best practice is a cooling‑system vacuum fill to 20–25 in‑Hg, then draw in premix. This prevents trapped air in the EGR cooler, heater core, and cylinder head passages and speeds bleeding on MX and X‑series engines.
4. Refill (gravity‑fill alternative)
   • Fill the surge tank slowly to the COLD line. Squeeze the upper radiator hose to purge air. Start and idle at ~1,000–1,200 rpm with the heater on. As the thermostat opens, the level will drop—top off to the COLD line. Watch for steady cabin heat (no surging) indicating the heater core is purged.
5. Bleed/verify
   • Run until both radiator hoses are hot and the cooling fan has cycled at least once. Check for leaks, then shut down and let fully cool. Recheck and top off to the COLD mark. Recheck again after the first long drive.

Notes

• Many T680 configurations do not have a dedicated bleeder screw; vacuum fill is strongly recommended for MX‑11/MX‑13 and Cummins X15 to avoid air pockets in the EGR cooler circuit.
• Never mix OAT ELC with conventional green IAT coolant. If mixing histories are unknown, perform a distilled‑water flush and refill with a single approved ELC.
• Maintain the surge tank cap to the correct rating (commonly ~15–20 psi; verify label on your tank). A weak cap can cause boil‑over and coolant loss.

Common cooling system issues (2017–2020 T680 generation)

• Radiator/cooler pack fouling: Debris in the condenser/CAC/radiator stack reduces airflow and raises temps on grades. Periodically clean the stack from the engine side forward.
• Surge tank and cap faults: Level sensor errors and cracked tanks or weak caps can cause false low‑coolant warnings or small leaks.
• Water pump seepage: Noted on both PACCAR MX‑13 and some Cummins applications; look for dried coolant trails at the weep hole and replace proactively.
• EGR cooler leaks: Coolant consumption with white steam from the exhaust or unexplained pressure. Pressure‑test the system and check for hydrocarbons in coolant if suspected.
• Thermostat or fan drive issues: Stuck thermostats or slipping fan hubs lead to intermittent overheating—monitor warm‑up time and commanded fan operation.
• Heater circuit air pockets: Long sleeper heater loops can trap air after service; vacuum fill or extended burping is necessary to restore steady cabin heat.
• Radiator tank seams: Plastic‑aluminum radiator tanks can seep at the crimp in high‑miles units; inspect along the end‑tank seams.

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