2018 Subaru Outback: Serpentine Belt Routing & Replacement

Quick Answer

• Belt Length & Rib Count: 1885mm (74.2") with 6 ribs
• OEM Belt Part Number: Subaru 809218520
• Aftermarket Belt Cross-References: Gates K060742, Dayco 5060740, Continental 4060742
• Automatic Tensioner Assembly Part Number: Subaru 23769AA05A
• Idler Pulley Part Number: Subaru 23770AA11A

Note: These part numbers apply to both the 2.5L H4 (FB25) and 3.6L H6 (EZ36) engines offered in the 2018 Outback.

Belt Routing

Before you remove the old belt, it is highly recommended that you take a clear photograph of the current belt routing from a couple of angles. This will be an invaluable reference to ensure the new belt is installed correctly.

The serpentine belt on the 2018 Subaru Outback follows a specific path around seven pulleys. Starting from the main crank pulley at the bottom center of the engine, the belt path is as follows:

1. Crankshaft Pulley: The belt travels up and to the passenger's side.
2. Air Conditioning Compressor: Wraps around the A/C compressor pulley.
3. Idler Pulley: Goes underneath the smooth idler pulley.
4. Alternator: Routes up and over the alternator pulley.
5. Power Steering Pump: Travels across to the driver's side to wrap around the power steering pump pulley.
6. Water Pump: Goes down and around the water pump pulley.
7. Tensioner Pulley: Finishes by routing under the tensioner pulley, which applies the necessary pressure to keep the belt taut.

How to Replace the Serpentine Belt

Replacing the serpentine belt on a 2018 Outback is a manageable task for a DIYer with the right tool. You will need a serpentine belt tool or a long 3/8" drive breaker bar to release the tension.

1. Safety First: Ensure the engine is cool to the touch before beginning work.
2. Locate the Tensioner: The automatic belt tensioner is located between the water pump and the crankshaft pulley. It has a 3/8" square hole in its body, designed for your tool.
3. Release Tension: Insert the 3/8" drive of your breaker bar or serpentine belt tool into the square hole on the tensioner body. Rotate the tensioner clockwise (towards the driver's side) to release the tension on the belt. The tensioner arm will swing away from the belt.
4. Remove the Old Belt: While holding the tensioner in the released position, carefully slip the old belt off one of the smooth, accessible pulleys like the idler or water pump pulley. Once it's free from one pulley, you can release the tensioner and remove the belt completely.
5. Install the New Belt: Referring to your photograph and the routing description above, begin threading the new belt around the pulleys, saving a smooth, easy-to-reach pulley for last (like the idler). Ensure the ribbed side of the belt makes contact with all grooved pulleys (Crank, A/C, Alternator, Power Steering) and the smooth back of the belt contacts the smooth pulleys (Idler, Water Pump, Tensioner).
6. Apply Tension: Once the belt is properly routed, use your breaker bar to rotate the tensioner clockwise again. Carefully slide the belt onto the final pulley. Double-check that the belt is centered on every pulley and not off by a groove.
7. Final Check: Slowly release the tensioner, allowing it to apply pressure to the new belt. Visually inspect the entire path one last time. Start the engine and let it run for about 30 seconds to ensure the belt is tracking correctly, then shut it off.

Replacement Interval

Subaru recommends inspecting the serpentine belt at regular service intervals (approximately every 30,000 miles) and replacing it as needed. While there is no strict replacement mileage, most belts last between 60,000 and 100,000 miles. Given the critical role of the belt in running the alternator, water pump, and power steering, it's wise to replace it proactively if it shows any signs of wear.

Signs of a Failing Belt or Tensioner

Be alert for these warning signs that your serpentine belt, tensioner, or idler pulley may need replacement:

• Squealing or Chirping Noises: This is the most common symptom, often worse on cold starts or in damp weather. It indicates the belt is slipping.
• Visible Wear: Inspect the belt for cracks, fraying, glazing (shiny spots on the surface), or missing ribs.
• Tensioner Noise: A rumbling or grinding noise coming from the tensioner area points to a failing bearing inside the pulley.
• "Bouncing" Tensioner Pulley: Watch the tensioner pulley with the engine running. If it is jumping or vibrating excessively instead of remaining steady, the spring mechanism is likely worn out.
• Accessory Malfunctions: If your power steering feels heavy, the battery light comes on (alternator not charging), or the engine temperature rises, the belt may have failed or is slipping severely.

If you're not comfortable performing this service yourself, you can find a trusted shop on Repairius.