2025 International MV Serpentine Belt Routing & Length

As an ASE-certified master technician, I know firsthand that commercial trucks like the 2025 International MV require regular maintenance to avoid costly downtime. The standard engine for the 2025 International MV is the reliable Cummins B6.7. This engine uses a heavy-duty serpentine belt system to drive vital accessories like the alternator, water pump, and A/C compressor.

Whether you are performing preventative maintenance in the fleet yard or handling an emergency roadside repair, having the correct part numbers and routing information is crucial.

Note: The International MV can be equipped with different engine options (such as the Cummins L9) and various accessory drive configurations. The information below reflects the most common Cummins B6.7 configuration with factory air conditioning. Always verify exact part numbers with your VIN at the dealership or parts supplier before purchasing.

Quick answer

• Belt Length: 70.8 inches (varies slightly by accessory package)
• Rib Count: 8-rib
• OEM Belt Part Number: Cummins 3972243 (International / Navistar equivalent)
• Aftermarket Cross-References: Gates K080708, Dayco 5080708, Continental Elite 4080708
• Auto-Tensioner Part Number: Cummins 3976831 (Aftermarket: Gates 38556)
• Idler Pulley Part Number: Cummins 3964588 (Aftermarket: Gates 36326)

Belt routing

Because the 2025 International MV features a medium-duty truck chassis, the engine bay is spacious, but the belt routing must be followed precisely to ensure proper accessory function and belt longevity. Always photograph or draw your existing belt routing before removal just in case your specific truck has a modified or custom PTO/accessory setup.

For the standard Cummins B6.7 accessory drive, follow this text-based routing path:

1. Start by looping the belt around the bottom of the Crankshaft Pulley.
2. Route the belt straight up and over the A/C Compressor Pulley.
3. Bring the belt down and under the smooth Idler Pulley.
4. Pull the belt up and over the Alternator Pulley.
5. Route the belt down and around the Water Pump Pulley.
6. Finally, slip the belt under the Auto-Tensioner Pulley (you will need to relieve the tension to slide it fully onto this final pulley) before it returns back to the Crankshaft Pulley.

How to replace the serpentine belt

Replacing the serpentine belt on the International MV's Cummins B6.7 is a straightforward process, but due to the heavy-duty nature of the tensioner, proper leverage is key.

Tools needed:

• 1/2-inch drive breaker bar or a heavy-duty serpentine belt tool.
• Gloves and safety glasses.

Step-by-step instructions:

1. Locate the tensioner: The automatic belt tensioner is located on the front of the engine, typically on the passenger side of the block.
2. Relieve tension: Insert the 1/2-inch drive breaker bar directly into the square slot on the tensioner arm. Rotate the tensioner counter-clockwise (or away from the belt) to release the tension.
3. Remove the old belt: Slip the belt off the easiest accessible pulley (usually the alternator or water pump). Carefully let the tensioner return to its resting position.
4. Route the new belt: Follow the routing instructions above, double-checking that the ribbed side of the belt seats perfectly into the grooves of the ribbed pulleys, and the smooth back of the belt rides flat against the idler and tensioner pulleys.
5. Apply tension: Pull the tensioner back with your breaker bar, slip the belt onto the final pulley, and gently release the tensioner to apply tension to the new belt.
6. Verify: Inspect all pulleys with a flashlight to ensure the belt is completely aligned before starting the truck.

Replacement interval

For commercial applications like the International MV, preventative maintenance is essential.

• Inspection: Inspect the belt and tensioner every 15,000 miles or during every routine oil change.
• Replacement: Replace the serpentine belt every 60,000 to 75,000 miles, or every 3 to 4 years, whichever comes first. Heavy idling or harsh environments (like construction sites or extreme heat) may require more frequent replacement.
• Tensioner & Idler: It is highly recommended to replace the automatic tensioner and idler pulley at the same time as the belt. A worn tensioner is the leading cause of premature belt failure.

Signs of a failing belt or tensioner

Don't wait for the belt to snap on the highway. Look out for these warning signs:

• Squealing or chirping noises: Especially on startup or when the A/C compressor engages. This usually indicates a stretched belt or a weak tensioner spring.
• Visible wear: Look for cracks across the ribs (more than 3 cracks per inch means it's time to replace), chunking, or frayed edges.
• Glazing: A shiny, hard appearance on the sides or ribs of the belt indicates overheating and slipping.
• Tensioner bouncing: While the engine is running, watch the tensioner. Minor vibration is normal, but excessive bouncing means the internal dampener has failed.
• Accessory issues: Intermittent power steering loss, battery charging warnings, or A/C blowing warm can all point to a slipping belt.

If you don't have the time or tools to perform this maintenance in-house, don't risk a breakdown on a commercial run. Find a trusted shop on Repairius.