DAY5120858

Includes (sold as a single belt):

• 1× heavy‑duty 12‑rib serpentine belt for ISX15/X15 engine accessory or fan drive.​
• Designed to wrap multiple pulleys (crank, fan hub, idlers, alternator, A/C compressor, etc.) with high tension and minimal slip.​
• Gold Label EPDM construction optimized for high torque diesel pulses and long service intervals.

Dayco 5120858 is a 12‑rib, 85.83‑inch Poly Rib Gold Label serpentine belt built for demanding Cummins ISX15/X15 front‑end accessory and fan drives on long‑haul tractors.

Fits Typical ISX15 / X15 Applications

• Peterbilt 367, 386, 387, 388, 389, 567, 579, 587 with ISM/ISX/X15 front‑end accessory drive (per Dayco HD coverage list).​
• Kenworth T660, T680, T700, T800, T880, W990 using ISX11.9/ISX15/X15 and 12‑rib 85.8" belt size.​
• Other PACCAR chassis where the OEM specifies 12PK2180 belt length for ISX/X15 cooling/accessory systems.