2018 GMC Sierra 2500HD — Serpentine Belt Routing & Length

As an ASE-certified master technician, I know that keeping your 2018 GMC Sierra 2500HD running strong means staying on top of essential maintenance items like the serpentine belt. Whether you are hauling heavy loads or using it as a daily driver, a broken belt will leave you stranded without power steering, a charging system, or an operating water pump.

Note: The specifications below cover the common 6.0L V8 Gas engine (L96/LC8) equipped with standard dual alternators or a single alternator setup. The 6.6L Duramax Diesel (L5P) will have different part numbers and dual-belt configurations.

Quick answer: Belt Specifications & Part Numbers (6.0L V8 Gas)

• Belt Length: 93.5 inches (standard single alternator setup)
• Rib Count: 6-rib
• OEM Belt Part Number: ACDelco 12626097
• Aftermarket Cross-References: Gates K060935, Dayco 5060935, Continental Elite 4060935
• Auto-Tensioner Part Number: ACDelco 38328 (or OEM 12609719) / Gates 38159
• Idler Pulley Part Number: ACDelco 38008 / Gates 36220

Belt routing

Because engine bays can be tight and memory is easily fooled, always take a clear photograph of your existing belt routing before you remove it. If the belt is already broken or missing, follow this text-based routing path for the 6.0L V8:

1. Start by looping the ribbed side of the belt around the bottom of the Crankshaft Pulley.
2. Bring the belt straight up so the smooth back side goes over the Water Pump Pulley.
3. Route the ribbed side down and around the Power Steering Pump Pulley on the lower driver’s side.
4. Bring it straight up to wrap around the Alternator Pulley on the top driver's side.
5. Route the belt across the engine, tucking the smooth back side under the Idler Pulley.
6. Bring the ribbed side down and around the A/C Compressor Pulley on the lower passenger side.
7. Finally, pull the belt up and over the Auto-Tensioner Pulley on the passenger side, returning down to the crankshaft.

How to replace the serpentine belt

Replacing the serpentine belt on a 2018 GMC Sierra 2500HD 6.0L is a straightforward job that you can tackle in your driveway.

1. Locate the tensioner: The automatic belt tensioner is located on the passenger side of the engine block.
2. Relieve the tension: Insert a dedicated serpentine belt tool or a standard 3/8" drive breaker bar directly into the square slot on the tensioner arm. Rotate the tensioner clockwise (towards the driver's side) to compress the internal spring and release tension on the belt.
3. Remove the old belt: While holding the tensioner open, slip the belt off the easiest accessible pulley (usually the alternator or idler pulley). Gently release the tensioner arm. Unthread the old belt from the remaining pulleys.
4. Install the new belt: Route the new belt following the path described in the section above, leaving the tensioner or idler pulley for last.
5. Apply tension: Once again, use your 3/8" breaker bar to rotate the tensioner. Slip the final loop of the belt over the remaining pulley.
6. Verify: Release the tensioner slowly. Double-check every pulley to ensure the ribs of the belt are seated perfectly within the grooves. Start the engine and observe the belt to ensure it is tracking completely straight.

Replacement interval

Modern EPDM (Ethylene Propylene Diene Monomer) serpentine belts are highly durable compared to the older neoprene belts. However, for a heavy-duty truck like the Sierra 2500HD, it is highly recommended to inspect the belt every 60,000 miles and replace it every 90,000 to 100,000 miles. If you frequently idle, tow heavy loads, or drive in extreme dusty or hot conditions, plan to replace it closer to the 75,000-mile mark. It is standard practice to replace the automatic tensioner and idler pulley at the same time, as their bearings wear out at a similar rate.

Signs of a failing belt or tensioner

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

• Squealing or Chirping: A high-pitched noise upon startup or acceleration usually indicates a stretched belt or a weak tensioner spring.
• Visible Wear: Look for missing ribs, deep cracks, fraying edges, or a shiny, glazed appearance on the ribbed side of the belt.
• Tensioner Bounce: While the engine is running, look at the tensioner arm. A millimeter of movement is normal, but excessive bouncing or rattling indicates the internal damper has failed.
• Accessory Issues: Heavy steering at low speeds, battery warning lights, or poor A/C performance can all point to a slipping belt.

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