DODGE TRUCKS:
• Dodge Ram 2500/Ram 3500 ISB 5.9L / ISB 6.7L Diesel (2003-2021)
CUMMINS INDUSTRIAL ENGINES:
• Cummins ISB 5.9/ISB 6.7/QSB 6.7 ISB/QSB 5.9/6.7L Diesel (2003-2021)
IMPORTANT:
Serpentine belt tensioner for Cummins ISB electronic 24-valve engines in both 5.9L (2003-2007) and 6.7L (2007-2021) displacements. Primary application is Dodge Ram 2500/3500 trucks, but also used in school buses, commercial vehicles, and industrial equipment with ISB/QSB engines.
Do NOT confuse with Cummins 5270678 — that is a different tensioner primarily for EPA13-certified B-platform engines. The 3947574 is the broader-application part covering both 5.9L and 6.7L ISB. Dodge/Chrysler cross-reference: 5086958AA. Mack cross-reference: 2428-89362. Alternate Cummins: 5297324.
IMPORTANT: This tensioner fits 2003+ electronic common-rail ISB engines only. Pre-2003 mechanical or VP44-injected 5.9L engines use a completely different belt routing and tensioner. Verify your engine serial number and CPL code.
Failure symptoms: belt squeal or chirp at startup, intermittent alternator undercharging, A/C compressor cycling issues, or visible tensioner arm wobble. A failing spring loses tension gradually — the belt may appear tight but slip under accessory load. Replace the serpentine belt at the same time.
⚠️ Verify engine CPL number — pre-2003 mechanical 5.9L ISB uses a different tensioner.
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