2018 GMC Acadia: Serpentine Belt Routing & Length

2018 GMC Acadia Serpentine Belt: A Complete Guide

Proper serpentine belt maintenance is critical to keeping your 2018 GMC Acadia running smoothly. This single belt drives multiple engine accessories, including the alternator, A/C compressor, water pump, and power steering pump. A worn or failing belt can leave you stranded.

This guide covers all the essential part numbers, routing information, and replacement tips you need for both the 2.5L 4-cylinder and 3.6L V6 engines.

Engine-Specific Information

The 2018 Acadia was offered with two engines, which use different belts and components. Ensure you have the correct parts for your vehicle.

Quick Answer: Belt & Component Part Numbers

Here are the key parts you'll need for a serpentine belt service. Part numbers can change, so always verify with your supplier before purchasing.

For the 2.5L I-4 Engine (LCV)

• Serpentine Belt Length & Rib Count: 85.9 inches, 6-rib
• OEM Belt PN: GM 12674921
• Aftermarket Belt Cross-References:
  • Gates: K060859
  • Dayco: 5060860
  • Continental: 4060859
• Automatic Belt Tensioner PN: GM 12670334 (Aftermarket e.g., Gates 39423)
• Idler Pulley PN: GM 12694901 (Aftermarket e.g., Gates 36173)

For the 3.6L V6 Engine (LGX)

• Serpentine Belt Length & Rib Count: 79.8 inches, 6-rib
• OEM Belt PN: GM 12684848 or 12674917
• Aftermarket Belt Cross-References:
  • Gates: K060798
  • Dayco: 5060800
  • Continental: 4060798
• Automatic Belt Tensioner PN: GM 12694900 (Aftermarket e.g., Gates 39422)
• Idler Pulley PN: GM 12694901 (Aftermarket e.g., Gates 38018)

Belt Routing

Since we cannot provide a visual diagram, it is essential that you take a clear photograph or draw a sketch of the current belt routing before you begin removal. This will be your best guide for installation.

The belt snakes around a series of grooved and smooth pulleys. The back (smooth side) of the belt wraps around smooth pulleys, while the ribbed side contacts grooved pulleys.

2.5L I-4 Belt Routing Path

The belt path for the four-cylinder engine is relatively simple:

1. Starts at the bottom Crankshaft Pulley (the main driver).
2. Wraps up and around the Idler Pulley.
3. Goes down and around the A/C Compressor pulley.
4. Travels up to the Alternator pulley at the top.
5. Comes down to the Belt Tensioner.
6. Returns to the Crankshaft Pulley.

3.6L V6 Belt Routing Path

The V6 engine has a more complex path:

1. Starts at the Crankshaft Pulley.
2. Wraps around the Water Pump pulley, which is centrally located.
3. Goes up and over the Power Steering Pump pulley.
4. Travels across to the Alternator pulley.
5. Comes down and around the Idler Pulley.
6. Goes down to the A/C Compressor pulley, located low on the passenger side.
7. Wraps up around the Belt Tensioner.
8. Returns to the Crankshaft Pulley.

How to Replace the Serpentine Belt

Replacing the belt is straightforward 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" or 1/2" drive breaker bar will also work.

1. Locate the Belt Tensioner: Find the automatic belt tensioner. It's a spring-loaded pulley designed to keep the belt tight. It will have a square 3/8" or 1/2" drive hole, or a hex feature on the pulley bolt to attach your tool.
2. Release Tension: Fit your serpentine belt tool or breaker bar into the tensioner. Pivot the tensioner against its spring pressure to loosen the belt. Do not try to loosen the center bolt of the pulley itself.
3. Remove the Old Belt: Once slack, carefully slip the belt off one of the highest and most accessible smooth pulleys, like the idler or alternator. Then, carefully unthread it from the rest of the pulleys.
4. Install the New Belt: Following the photo or diagram you made earlier, thread the new belt around the pulleys, saving one easily accessible pulley for last.
5. Final Step: Release the tensioner again and slip the belt over the final pulley. Double-check that the belt is correctly seated in the grooves of every ribbed pulley and centered on the smooth pulleys. A misaligned belt will shred itself quickly.

Replacement Interval

Modern serpentine belts are durable. While there is no universally mandated replacement interval from GMC, a general guideline is to inspect the belt during every oil change and plan for replacement every 60,000 to 90,000 miles. Environmental factors like extreme heat or cold can shorten this lifespan. If the belt tensioner or an idler pulley is being replaced, always install a new belt at the same time.

Signs of a Failing Belt or Tensioner

Listen and look for these warning signs:

• Squealing or Chirping Noises: This is the most common sign, especially on startup or when the A/C is turned on.
• Visible Wear: Inspect the belt for cracks, fraying, glazing (shiny spots), or missing ribs.
• Tensioner Noise: A grinding or rattling from the tensioner indicates a failing bearing in its pulley.
• Tensioner Movement: If the tensioner arm is vibrating erratically while the engine is running, its internal spring is likely weak and it needs to be replaced.
• Accessory Problems: Dimming headlights (alternator), lack of A/C cooling, or overheating (water pump) can all be caused by a slipping or broken belt.

Replacing your serpentine belt is a manageable DIY job that prevents major headaches down the road. If you're not comfortable performing this service, Repairius can help.

Find a trusted shop on Repairius.