57-861758Q Serpentine Belt for Mercruiser V6 V8 Alpha | JLM Marine

Serpentine Belt for Mercruiser V6 & V8 Alpha Engines (1996-1999) – Replaces 57-861758Q

This serpentine belt is designed for Mercruiser Alpha sterndrive engines equipped with V6 (4.3L) and V8 (5.0L, 5.7L) configurations manufactured between 1996 and 1999 (serial numbers 0L618999 and below). It is compatible with Alpha engines featuring standard cooling and power steering systems, ensuring reliable performance for a wide range of Mercruiser applications.

Direct Replacements: Mercruiser 861758Q, 57-861758, 57-861758Q; Sierra 18-15116.

• Fits 4.3L, 5.0L, and 5.7L Mercruiser Alpha engines with standard cooling and power steering
• Compatible with both Gen+ and EFI configurations across multiple model years
• Precision-engineered to OEM specifications for optimal belt tension and longevity

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

• 1 × Serpentine Belt (57-861758Q)

Installation Guide

1. Disconnect the battery: Before beginning, disconnect the negative battery terminal to ensure safety during installation.
2. Locate the serpentine belt routing diagram: Consult your engine manual or the diagram typically found on the engine cover to understand the correct belt path.
3. Release belt tension: Using a wrench or socket on the tensioner pulley, rotate it to relieve tension on the old belt. Some models may have a spring-loaded automatic tensioner.
4. Remove the old belt: Slide the old serpentine belt off the pulleys, noting the routing pattern if no diagram is available.
5. Inspect pulleys and tensioner: Check all pulleys for damage, wear, or misalignment. Ensure the tensioner operates smoothly and provides adequate spring tension.
6. Route the new belt: Starting at the crankshaft pulley, thread the new serpentine belt around each pulley following the routing diagram exactly.
7. Engage the tensioner: Rotate the tensioner again and slip the belt onto the final pulley (usually the tensioner or alternator). Release the tensioner slowly to apply proper tension.
8. Verify belt alignment: Ensure the belt is seated correctly in all pulley grooves and is not twisted or misaligned.
9. Reconnect the battery: Reattach the negative battery terminal.
10. Test operation: Start the engine and observe the belt for proper tracking and tension. Listen for any unusual noises such as squealing or slapping.
11. Check tension after initial run: After running the engine for a few minutes, shut it off and visually confirm the belt has not slipped or loosened.

Troubleshooting & FAQ

How do I confirm this belt fits my Mercruiser engine?
Verify your engine model, displacement (4.3L, 5.0L, or 5.7L), and serial number against the compatibility table above. This belt is designed for Alpha engines with standard cooling and power steering built between 1996 and 1999 (serial 0L618999 and below). If your engine has different accessories or a different cooling system, this belt may not fit.

What are the signs that my serpentine belt needs replacement?
Common indicators include visible cracks, fraying, glazing, or chunks missing from the belt surface. You may also hear squealing noises during startup or acceleration, or notice accessories like the alternator or power steering pump not functioning properly. Replace the belt immediately if any of these symptoms occur.

How often should I replace the serpentine belt?
Mercruiser recommends inspecting the serpentine belt annually and replacing it every 3-5 years or sooner if signs of wear appear. Operating conditions such as saltwater exposure, high temperatures, and frequent use can accelerate wear and may require more frequent replacement.

Can I use this belt on Bravo drive engines?
This belt is primarily designed for Alpha sterndrive engines, though some Bravo configurations within the listed serial ranges may be compatible (such as the 350 MAG MPI ALPHA/BRAVO and certain Mag Bravo 4V models). Always verify your specific engine model and serial number in the compatibility table before purchasing.

What is the difference between this aftermarket belt and the OEM Mercruiser belt?
This is an aftermarket replacement part built to OEM specifications using comparable-grade materials. It is designed to deliver the same fit, performance, and durability as the original Mercruiser 57-861758Q belt, but at a more competitive price point. Production occurs in an ISO9002-certified facility with rigorous quality control.

Why is my new serpentine belt squealing?
Squealing typically indicates improper tension, misalignment, or contamination (oil/coolant) on the belt or pulleys. Check that the belt is routed correctly, the tensioner is functioning properly, and all pulleys are clean and aligned. If squealing persists, inspect the tensioner spring for weakness or failure.

Is this an OEM part 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.