Serpentine Belt Idler Pulley – Fits Volvo Penta 4.3/5.0/5.7/8.1L (Replaces 3861009)

$69.99

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Product Details

This replacement Serpentine Belt Idler Pulley is engineered for Volvo Penta gasoline marine engines, including the 4.3L, 5.0L, 5.7L, and 8.1L series (GXi, Gi, GXiE, OSi/OSXi models) from approximately 1999–2012. It ensures the serpentine belt system maintains correct tension for optimal performance.

It serves as a direct interchange for Volvo Penta part number 3861009.

Installs directly as a bolt-on replacement.
Durable metal housing designed for the marine environment.
Maintains proper belt tension on the serpentine system to prevent slippage.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Volvo Penta	3861009

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This part is designed for compatibility with the following Volvo Penta sterndrive engines.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.
Volvo Penta	4.3GXiE	225	4-Stroke	1999–2012	3861009
Volvo Penta	5.0GXi	270	4-Stroke	1999–2012	3861009
Volvo Penta	5.7Gi	280	4-Stroke	1999–2012	3861009
Volvo Penta	5.7GXi	320	4-Stroke	1999–2012	3861009
Volvo Penta	5.7OSi	280	4-Stroke	1999–2012	3861009
Volvo Penta	5.7OSXi	320	4-Stroke	1999–2012	3861009
Volvo Penta	8.1Gi	375	4-Stroke	1999–2012	3861009
Volvo Penta	8.1GiE	420	4-Stroke	1999–2012	3861009

Technical Specs

Product Type: Serpentine Belt Idler Pulley
Installation: Direct replacement, bolt-on
Housing Material: Metal
Dimensions: 3.5 inches (88.9 mm) diameter
Fitting Type: Direct bolt-on
Other Technical Attributes: Maintains proper belt tension on serpentine system

What’s in the Box

1 x Serpentine Belt Idler Pulley (Replaces 3861009)

Installation Notes

Disconnect the battery terminals to ensure safety.
Locate the serpentine belt tensioner and use an appropriate tool to release the tension on the belt. Slide the belt off the idler pulley.
Unbolt and remove the old idler pulley. Note the orientation and placement of any washers or spacers.
Clean the mounting surface on the engine bracket.
Mount the new idler pulley, ensuring it is correctly aligned. Torque the bolt to the manufacturer's specification.
Carefully reinstall the serpentine belt, ensuring it is routed correctly around all pulleys.
Slowly release the tensioner to apply pressure to the belt. Double-check belt alignment and tension.
Reconnect the battery.
Start the engine and listen for any unusual noises. Visually inspect the pulley and belt for proper operation.

Troubleshooting & FAQ

How do I know if my idler pulley needs to be replaced?

Common signs of a failing idler pulley include a persistent squealing, chirping, or grinding noise from the engine bay, visible wobble or physical damage to the pulley itself, or uneven/accelerated wear on your serpentine belt.

Is this a grooved or smooth idler pulley?

This is a smooth idler pulley. It is designed to make contact with the back (smooth side) of the serpentine belt.

What is the main function of an idler pulley?

An idler pulley's job is to guide and maintain tension on the engine's serpentine belt, ensuring that engine accessories like the alternator, water pump, and power steering pump are driven correctly.

How often should I replace my idler pulley?

While there is no fixed interval, it is best practice to inspect idler pulleys during routine service. Many mechanics recommend replacing the idler pulley and tensioner assembly whenever you replace the serpentine belt.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement, not an OEM component.
Professional installation is recommended for safety and performance.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

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