865598 Serpentine Belt Pulley for MerCruiser | JLM Marine

Serpentine Belt Pulley for MerCruiser – Fits 4.3L, 5.0L, 5.7L, 5.8L, 6.2L, 8.1L Engines

This Serpentine Belt Idler Pulley is designed for MerCruiser inboard and stern drive engines, including 4.3L, 5.0L, 5.7L, 5.8L, 6.2L, and 8.1L models with Alpha and Bravo drives. Engineered to maintain proper belt tension and reduce vibration, this flat idler pulley ensures reliable performance in demanding marine environments.

This aftermarket pulley directly replaces OEM part numbers 8M6500024, 865598, 818382, and 710-8M6500024, providing a cost-effective solution without compromising quality or fitment.

• Pulley Size: 3-3/16" flat idler design for serpentine belt systems
• Application: Engine idler pulley for MerCruiser stern drive and inboard engines
• Direct Fit: Designed to OEM specifications for seamless installation

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here's a guide to help you identify your engine's serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

Your package includes:

• 1 × Serpentine Belt Idler Pulley (3-3/16", Flat Design)

Installation Guide

1. Disconnect the battery to prevent accidental engine start during installation.
2. Locate the serpentine belt routing diagram on your engine or in your service manual. Take a photo for reference before removal.
3. Release belt tension by loosening the tensioner or adjusting bolt, then carefully slide the serpentine belt off the pulleys.
4. Remove the mounting bolt securing the old idler pulley to the engine bracket.
5. Inspect the mounting bracket and bolt for wear, corrosion, or damage; replace if necessary.
6. Install the new idler pulley onto the mounting bracket, ensuring proper alignment.
7. Hand-tighten the mounting bolt first, then torque to manufacturer specifications (refer to your service manual).
8. Route the serpentine belt back onto all pulleys following the diagram or photo you referenced earlier.
9. Check belt alignment and tension to ensure the belt sits centered on all pulleys without slack or excessive tightness.
10. Reconnect the battery and start the engine briefly to verify smooth operation.
11. Listen for unusual noises such as squealing or rattling, which may indicate misalignment or improper tension.
12. Perform a final inspection after the first few hours of operation to confirm the pulley and belt remain properly seated.

Troubleshooting & FAQ

How do I confirm this pulley fits my MerCruiser engine?
Verify your engine displacement (4.3L, 5.0L, 5.7L, 5.8L, 6.2L, or 8.1L) and check that your current pulley measures 3-3/16" and is a flat idler type. Cross-reference your existing OEM part number (865598, 8M6500024, 818382, or 710-8M6500024) with the compatibility table above.

What are the signs that my idler pulley needs replacement?
Common symptoms include squealing or chirping noises from the belt area, visible wear or wobble in the pulley, excessive belt wear or fraying, or rough bearing rotation when spun by hand with the belt removed.

How often should I replace the serpentine belt idler pulley?
Inspect the idler pulley during routine maintenance or whenever replacing the serpentine belt. Replace it if you notice roughness, play, or noise, or approximately every 3–5 years depending on operating hours and conditions.

Can I use this pulley if my engine has a different belt configuration?
This pulley is designed specifically for serpentine belt systems on the listed MerCruiser engines. If your engine uses a V-belt system or a different pulley diameter, this part will not be compatible.

Is this an OEM pulley or an aftermarket replacement?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.