2018 Ford F-350 Super Duty — Serpentine Belt Routing & Length

Quick answer

• Belt length:
  • 6.2L gasoline V8 (single belt): length is VIN/option-specific; confirm by VIN or old-belt measurement
  • 6.7L Power Stroke diesel: main drive belt length is VIN/option-specific; A/C often uses a separate stretch belt
• Rib count:
  • 6.2L gas: 6‑rib serpentine belt (single belt system)
  • 6.7L diesel: 8‑rib main serpentine belt plus a separate A/C stretch belt (rib count varies by configuration)
• OEM Ford belt part number (base): 8620 (full PN is VIN-specific; verify in Ford catalog)
• Aftermarket cross‑references (format guidance; verify exact PN by engine/VIN):
  • Gates Micro‑V: K06xxxx (6‑rib gas) / K08xxxx (8‑rib diesel main)
  • Dayco Poly Rib: 506xxxx (6‑rib) / 508xxxx (8‑rib)
  • Continental: 406xxxx (6‑rib) / 408xxxx (8‑rib)
• Automatic belt tensioner (Ford base PN): 6B209 (assembly; VIN‑specific complete PN)
• Idler pulley (Ford base PN): 8678 (VIN‑specific complete PN)

Note: The exact belt length and part numbers vary with engine (6.2L gas vs 6.7L diesel), A/C, dual alternators, ambulance/plow/upfitter packages, and emission drive options. Always verify by VIN or with your parts supplier before ordering. Never rely solely on visual similarity.

Belt routing

Before removal, take a clear photo of your existing belt path and, if present, both belts on diesel models. Many trucks have an under‑hood decal; if yours is missing, use the text routing below.

Typical single‑belt routing (commonly 6.2L gas) described in order of travel:

1. Start at the crankshaft pulley (harmonic balancer) at the bottom.
2. From the crank pulley up to the A/C compressor.
3. Across to the nearest idler pulley.
4. Up and over the alternator pulley.
5. Down to the power steering pump.
6. Around the water pump pulley.
7. Finally around the automatic tensioner, then back to the crank pulley to complete the loop.

Important diesel note: Many 6.7L Power Stroke engines use two belts—a main 8‑rib belt for alternator/power steering/water pump and a separate stretch belt that runs directly from the crank to the A/C compressor. If your truck has the separate A/C belt, the above single‑belt path will not apply to the A/C drive. Route the main belt per the under‑hood decal and install the A/C stretch belt last using the proper stretch‑belt tool.

How to replace the serpentine belt

Tools and prep:

• Serpentine belt tool or a 3/8" (or 1/2", as equipped) breaker bar to unload the tensioner
• Flashlight and your phone camera (take photos before removal)
• New belt(s) matched to your VIN; on 6.7L, also obtain the A/C stretch belt if equipped

Steps:

1. Disconnect the negative battery cable if access is tight near the fan or if working around the alternator.
2. Note the routing (photo the existing installation). Identify the automatic tensioner—look for a square 3/8" or 1/2" drive pocket.
3. Rotate the tensioner to relieve tension. Slip the belt off a smooth, easy‑to‑reach pulley (often the idler or alternator).
4. Remove the old belt. On 6.7L engines with a separate A/C belt, cut the old A/C stretch belt off—do not pry it off the pulleys.
5. Compare the new belt(s) length and rib count to the old belt(s).
6. Route the new belt according to the path above/under‑hood decal, leaving the easiest pulley for last. Ensure ribs are fully seated in each grooved pulley.
7. Rotate the tensioner again and slip the belt over the last pulley. Slowly release the tensioner to apply tension.
8. For A/C stretch belts (diesel where equipped), use a stretch‑belt installation tool and follow the belt’s directional arrows.
9. Double‑check alignment. Start the engine and observe for 20–30 seconds. The belt should track smoothly with no chirp or wander.

Replacement interval

• Normal service: inspect every 15,000 miles; replace around 60,000–100,000 miles or 6 years, whichever comes first.
• Harsh service (towing, plowing, high‑idle, dusty or hot climates): inspect at every oil change; replacement closer to 60,000 miles is prudent.
• Replace the automatic tensioner and idler(s) if the belt shows repeat noise/wear or if pulleys are rough, noisy, or misaligned. It’s common to service the tensioner and idlers with the second belt replacement.

Signs of a failing belt or tensioner

• Belt:
  • Cracking across ribs, fraying edges, missing chunks, glazing/shiny ribs, or contamination with coolant/oil
  • Chirp/squeal on startup or with A/C load
  • Visible stretch or belt riding out of the pulley grooves
• Tensioner/idlers:
  • Belt flutter, vibration, or wandering
  • Ticking/rumbling from idler bearings
  • Tensioner arm jerking or not returning smoothly when unloaded
  • Charging, steering assist, or cooling problems at idle (slip under load)

Engine and option variations that affect part numbers

• 6.2L gasoline V8: typically a single 6‑rib serpentine belt; length varies with with/without A/C and HD electrical options.
• 6.7L Power Stroke diesel: usually an 8‑rib main belt plus a separate A/C stretch belt; configurations vary with single vs dual alternators and upfitter packages.

Because these variations directly change belt length and hardware, confirm the exact part numbers by VIN with a Ford dealer or a reputable parts supplier. Provide your engine (6.2L or 6.7L), A/C presence, and whether you have dual alternators.

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