2021 Mercedes-Benz Sprinter Serpentine Belt Guide

Quick Answer

• Engine Options: 2.1L 4-cylinder (OM651), 3.0L V6 (OM642)
• Belt Length & Rib Count:
  • 2.1L 4-cyl: 2200mm (86.6"), 7-rib
  • 3.0L V6: 1730mm (68.1"), 7-rib
• OEM Belt Part Numbers:
  • 2.1L 4-cyl: A0029934396
  • 3.0L V6: A0039937296
• Aftermarket Belt Cross-References:
  • 2.1L 4-cyl: Gates K070865, Continental 4070865
  • 3.0L V6: Gates K070680, Continental 4070680, Dayco 5070680
• Auto-Tensioner Part Number:
  • 2.1L 4-cyl: 6512001970
  • 3.0L V6: 6422001370
• Idler Pulley Part Number:
  • 2.1L 4-cyl: 6512000470 (Grooved), A6112020019 (Smooth)
  • 3.0L V6: 6422020719 (Grooved), 6422020119 (Smooth)

Belt Routing

Before you remove the old serpentine belt, always take a clear photograph of the belt's path. This will be your most valuable reference. The routing can differ based on your engine and installed options.

For a typical 2021 Sprinter, the belt winds its way around all the engine-driven accessories. Starting from the main crankshaft pulley at the bottom of the engine, the path generally follows this sequence:

1. Crankshaft Pulley (ribbed side of the belt)
2. Air Conditioning Compressor (ribbed side)
3. Idler Pulley (smooth side)
4. Alternator (ribbed side)
5. Power Steering Pump (ribbed side)
6. Water Pump (smooth side)
7. Tensioner Pulley (smooth side), which maintains pressure on the belt.

Again, your vehicle's specific routing may vary slightly. Refer to your photo to ensure the new belt is installed correctly. An incorrectly routed belt can cause damage to the belt and the accessories.

How to Replace the Serpentine Belt

Replacing the serpentine belt on a Sprinter requires a few specific tools. You will need a serpentine belt tool, which is a long, thin bar with various socket attachments, or a long-handled 3/8" breaker bar.

1. Locate the Tensioner: Find the automatic belt tensioner. It's a spring-loaded pulley designed to keep the belt tight. You will see a square hole (often 3/8") or a hex-shaped boss on the body of the tensioner arm.

2. Release Tension: Insert your breaker bar or serpentine belt tool into the designated spot on the tensioner. Carefully pull or push on the tool to move the tensioner pulley away from the belt, releasing the tension. This requires a bit of force.

3. Remove the Old Belt: While holding the tensioner in the released position, slip the old belt off one of the smooth pulleys, like the idler or water pump pulley. Once it's free, you can slowly release the tensioner and remove the belt completely.

4. Install the New Belt: Referring to the photo you took earlier, carefully route the new belt around all the pulleys, leaving a smooth pulley for last (like the tensioner or idler). Double-check that the ribbed side of the belt is making contact with ribbed pulleys and the smooth back of the belt is touching the smooth pulleys.

5. Apply Tension: Release the tension on the tensioner arm again and slip the belt over the final pulley. Once the belt is in place on all pulleys, slowly and carefully release the tool, allowing the tensioner to apply pressure to the new belt. Visually inspect the entire path one last time to ensure it is seated correctly in every groove.

Replacement Interval

Mercedes-Benz recommends inspecting the serpentine belt at regular service intervals. While there isn't a strict mileage replacement rule, it's wise to replace it as a preventative measure every 60,000 to 90,000 miles. A belt's lifespan can be affected by operating conditions, such as extreme temperatures and exposure to oil or other fluids.

Signs of a Failing Belt or Tensioner

Be alert for signs that your serpentine belt, tensioner, or idler pulleys are on their way out. Ignoring these warnings can lead to a breakdown.

• Squealing or Chirping Noises: This is the most common sign. The noise may be constant or may change with engine speed. It often points to a worn, glazed belt or a failing tensioner that isn't providing enough pressure.
• Visible Wear: Inspect the belt for cracks, fraying, missing ribs, or a shiny, glazed appearance. Any visible damage means the belt needs immediate replacement.
• Tensioner or Pulley Noise: A grinding or rumbling sound from the engine bay could indicate a worn-out bearing in the tensioner or an idler pulley. If you see the tensioner arm vibrating or jumping erratically while the engine is running, it's a sign that the spring mechanism is failing.
• Accessory Problems: If your power steering feels heavy, the battery isn't charging (alternator), or the engine is overheating (water pump), the belt could be slipping or may have already broken.

If you're not comfortable performing this service yourself, let us help. Find a trusted shop on Repairius.