Serpentine Belt – Fits MerCruiser 4.3L, 5.0L, 5.7L V6/V8 Alpha Engines (Replaces 57-861758Q)
Serpentine Belt – Fits MerCruiser 4.3L, 5.0L, 5.7L V6/V8 Alpha Engines (Replaces 57-861758Q) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Serpentine Belt – Fits MerCruiser 4.3L, 5.0L, 5.7L V6/V8 Alpha Engi...
Product Details
This Serpentine Belt – Fits MerCruiser 4.3L, 5.0L, 5.7L V6/V8 Alpha Engines (Replaces 57-861758Q) is engineered for MerCruiser 4.3L V6, 5.0L V8, and 5.7L V8 Alpha engines from 1996–1999 (serial numbers OF803000-OL618999) equipped with standard cooling and a 5-3/4" power steering pulley. It's designed to restore proper function to your engine's accessory drive system.
It serves as a direct replacement for Mercury/MerCruiser part numbers 57-861758, 57-861758Q, 861758, 861758Q, and Sierra 18-15116.
- Drives engine accessories like the alternator and power steering pump.
- Strengthened main structure provides resistance to tension and wear.
- Built for marine environments with standard cooling systems.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/MerCruiser | 57-861758 |
| Mercury/MerCruiser | 57-861758Q |
| Mercury/MerCruiser | 861758 |
| Mercury/MerCruiser | 861758Q |
| Sierra | 18-15116 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser models, verify your engine's serial number falls within the specified range to ensure correct fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 4.3L Alpha | 190-220 | 4-Stroke | 1996–1999 | 57-861758Q | Serial #OF803000-OL618999 |
| MerCruiser | 5.0L Alpha | 230-260 | 4-Stroke | 1998–1999 | 57-861758Q | Serial #OL012052-OL618999 |
| MerCruiser | 5.7L Alpha | 250-300 | 4-Stroke | 1997–1999 | 57-861758Q | Serial #OK001506-OL618999 |
| MerCruiser | 350 Mag Alpha | 300-350 | 4-Stroke | 1997–2004 | 57-861758Q | Serial #OK001501-OL618999 |
Technical Specs
- Product Type
- Serpentine Belt
- Installation
- Engine Accessory Drive
- Belt Type
- Ribbed Serpentine
- Belt Length
- 219.7 cm (86.5")
- Belt Width
- 2.06 cm (0.81")
- Material
- Superior Rubber Compound
- Weight
- 0.56-0.65 lbs (0.25-0.30 kg)
- Color
- Black
- Application
- Standard Cooling with Power Steering
- Compatibility
- 5-3/4" Power Steering Pulley
- Warranty
- 1 year against manufacturing defects
- Other Technical Attributes
- Tension-resistant with strengthened main structure
What’s in the Box
- 1 x Serpentine Belt (57-861758Q)
Installation Notes
- Ensure the engine is off and completely cool. Disconnect the negative battery cable for safety.
- Locate the serpentine belt tensioner. Using a socket or wrench, rotate the tensioner to release pressure on the belt.
- While holding the tensioner, carefully slip the old belt off the pulleys. Note the belt routing path before removal; taking a photo can be helpful.
- Inspect all pulleys for wobble, damage, or contamination (oil, coolant). Clean them before installing the new belt.
- Route the new belt according to the diagram for your engine model, starting with the crankshaft pulley.
- Once the belt is routed around all pulleys except the tensioner, rotate the tensioner again and slide the belt into place.
- Slowly release the tensioner to apply pressure to the new belt. Double-check that the belt is correctly seated in all pulley grooves.
- Reconnect the battery cable, start the engine, and briefly observe to ensure the belt is tracking properly.
Troubleshooting & FAQ
How do I know this belt is the right one for my engine?
Verify your engine model, year, and serial number against the compatibility table. This belt is specifically for MerCruiser V6/V8 Alpha engines from 1996–1999 with a 5-3/4" power steering pulley and standard cooling. If your serial number is outside the listed ranges, this belt will not fit.
What are signs that my old serpentine belt needs replacing?
Common signs of a failing belt include visible cracks, fraying, or glazing on the belt's surface. You may also hear a high-pitched squealing or chirping sound from the engine, particularly on startup or when the engine is under load. Dimming lights or a battery warning light can also indicate a slipping belt is failing to drive the alternator properly.
How often should a marine serpentine belt be replaced?
It's best to consult your engine's service manual for specific maintenance intervals. As a general rule, inspect the belt annually for signs of wear and consider replacement every 3-5 years or 300-500 operating hours, depending on usage and conditions.
Can I use this belt with a high-output alternator?
This belt is designed as a direct replacement for OEM specifications and standard accessory loads. If you have installed a high-output alternator or other non-standard accessories, you may require a heavy-duty or specialized belt to prevent slippage and premature wear.
What is the difference between this and the OEM belt?
This is an aftermarket part designed to meet or exceed original equipment manufacturer (OEM) specifications for fit, form, and function. It offers comparable performance and durability to the original MerCruiser belt at a more competitive price point.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility and batch-inspected for consistency.
Shipping speed & cost?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options will appear at checkout where available.
Warranty & returns?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact our support team with your order details. Returns are accepted within our standard window, provided the item is unused and in its original condition. See our full policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against 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, typically arriving in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or quality control.
Payment & Security
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