2023 GMC Sierra 2500HD: Serpentine Belt Replacement Guide

Quick Answer: Serpentine Belt Specifications

Note that the 2023 GMC Sierra 2500HD is available with two different engines: a 6.6L V8 gasoline engine and a 6.6L V8 Duramax turbo-diesel. These engines use different serpentine belts and components.

For the 6.6L V8 Gas Engine (L8T):

• Belt Length & Rib Count: 93.5 inches, 6-rib
• OEM Belt PN: GM 12686192
• Aftermarket Cross-References: Gates K060935, Dayco 5060935, Continental 4060935
• Auto-Tensioner Assembly PN: GM 12678763
• Idler Pulley PN: GM 12686193

For the 6.6L V8 Duramax Diesel Engine (L5P):

The Duramax engine utilizes a primary serpentine belt for most engine accessories and a secondary, smaller v-belt for the A/C compressor.

• Main Serpentine Belt: GM 12678762 (Gates K061000, Dayco 5061000)
• A/C Compressor V-Belt: GM 12658169 (Gates K040360)
• Main Auto-Tensioner Assembly PN: GM 12690928
• Idler Pulley PN: GM 12626023

Belt Routing

Before you remove the old serpentine belt, it is crucial to understand how it is routed. A mistake here can lead to an improperly running engine, accessories that don’t work, or damage to the new belt. We always recommend taking a clear photograph of the belt's path before you begin removal.

For the 6.6L Gas V8, the belt follows this general path, starting from the main crankshaft pulley at the bottom of the engine:

1. From the Crankshaft Pulley, the belt travels up and around the A/C Compressor pulley.
2. From the A/C Compressor, it moves to the stationary Idler Pulley.
3. Next, it wraps around the Alternator pulley.
4. It then goes down to the Power Steering Pump pulley.
5. The belt continues to the Water Pump pulley.
6. Finally, it travels around the Tensioner Pulley, which maintains the correct belt tension, and back to the crankshaft.

The routing for the Duramax diesel engine is similar but involves more components. Again, photograph the layout before disassembly.

How to Replace the Serpentine Belt

Replacing the serpentine belt is a manageable task for a DIYer with the right tool. You will need a serpentine belt tool, which is a long, thin ratchet with various socket and crowfoot attachments. In many cases, a standard 3/8-inch or 1/2-inch drive breaker bar will also fit into the square hole on the belt tensioner.

1. Safety First: Ensure the engine is completely cool.
2. Locate the Tensioner: Find the automatic belt tensioner. It’s a spring-loaded pulley designed to keep the belt tight. It will have a square hole or a raised hex head for your tool to grip.
3. Release Tension: Insert your breaker bar or serpentine belt tool into the tensioner. Rotate the tensioner arm to release the pressure on the belt. This does not require a large amount of force.
4. Remove the Old Belt: While holding the tensioner in the released position, carefully slip the old belt off one of the pulleys (the alternator or idler pulley is usually easiest).
5. Inspect Pulleys: With the belt off, spin each pulley by hand (except the crankshaft, of course). They should spin freely and quietly. A gritty, noisy, or wobbly pulley indicates a failing bearing, and the component (idler, tensioner, or accessory) should be replaced.
6. Install the New Belt: Following the photograph you took or your routing diagram, carefully thread the new belt around the pulleys. Start with the crankshaft pulley and work your way through the path, saving the tensioner or another smooth pulley for last.
7. Apply Tension: Once the belt is routed correctly on all grooved pulleys, release the tensioner arm, applying pressure to the new belt. Double-check that the belt is centered in the grooves of every pulley.

Replacement Interval

Modern serpentine belts are durable. There is no strict replacement interval from GMC, but a general industry consensus is to inspect the belt during routine oil changes after 60,000 miles. A full replacement is recommended between 90,000 and 120,000 miles, or whenever it shows signs of wear. Proactive replacement can prevent a breakdown, as a failed belt will immediately disable your vehicle.

Signs of a Failing Belt or Tensioner

Be alert to the warning signs of a worn belt or a failing tensioner. Ignoring them can leave you stranded.

• Squealing Noises: A high-pitched squeal upon startup or during operation often points to a slipping, glazed, or contaminated belt.
• Visible Wear: Look for cracks, fraying, glazing (shiny spots), or missing chunks of the ribbed section.
• Tensioner Noise: A rattling or grinding noise coming from the tensioner area indicates a failing bearing in the tensioner pulley.
• "Fluttering" Belt: If you see a section of the belt vibrating or "fluttering" rapidly while the engine is running, it often means the spring inside the tensioner is weak and can no longer maintain adequate pressure.
• Accessory Malfunctions: Since the belt drives the alternator, power steering, and water pump, a failing belt can cause dimming lights, difficult steering, or a rise in engine temperature.

Find a trusted shop on Repairius.