Part Number Interchange
| Brand / Reference | Part Number |
|---|---|
| Mercury / MerCruiser | 57-8638763 |
| Mercury / MerCruiser | 8638763 |
| Mercury / MerCruiser | 57-865615-003 |
| Mercury / MerCruiser | 865615003 |
| Mercury / Quicksilver | 865615Q03 |
| Mercury / Quicksilver | 57-865615Q03 |
| Sierra | 18-15100 |
| Sierra | 18-15103 — verify independently |
Important: Mercury’s catalog identifies 865615Q03 as the replacement for 57-8638763. Confirm other aftermarket interchange numbers before purchasing.
Product Specifications
| Specification | Details |
|---|---|
| Product | Marine Serpentine Belt |
| Primary Reference | 57-8638763 |
| Current OEM Replacement Reference | 865615Q03 |
| Belt Length of OEM Equivalent | 2,704 mm / approximately 106.5 inches |
| Engine Type | Gasoline V6 / V8 |
| Engine Sizes | 4.3L, 5.0L, 5.7L, select 6.2L |
| Drive System | Select Alpha / Bravo |
| Package Contents | 1 Serpentine Belt |
| Advertised Package Weight | Approximately 350 g |
| Brand of Supplied Aftermarket Belt | Not specified |
The 2,704 mm measurement is published for the Mercury/Quicksilver 865615Q03 replacement. Confirm the supplied aftermarket belt matches that specification before listing it as an exact replacement.
Why Marine Serpentine Belt Maintenance Matters
Marine engines operate under sustained loads, often at higher throttle settings for extended periods.
A deteriorated accessory belt may affect the operation of essential engine-driven components.
Depending on the engine’s configuration, a failed belt may contribute to:
- Loss of alternator charging
- Reduced circulating water pump operation
- Reduced seawater pump operation
- Engine overheating
- Unexpected downtime on the water
The exact consequences depend on which accessories are driven by the belt.
Inspect the accessory drive system regularly and replace damaged components before operating the boat.
Signs Your MerCruiser Belt Needs Replacement
Watch for:
- Squealing or chirping noises
- Frayed belt edges
- Damaged or missing ribs
- Glazed belt surfaces
- Visible cracking or deterioration
- Excessive belt vibration
- Abnormal pulley movement
- Belt slipping
- Cooling system or charging system problems
A worn tensioner, damaged pulley or failing accessory bearing can cause similar symptoms.
Installation Guidance
- Shut down the engine and secure the boat.
- Disconnect or isolate the engine starting system according to the service manual.
- Locate the engine’s accessory belt routing diagram.
- Verify the original belt part number and engine serial number.
- Inspect the belt tensioner, pulleys and driven accessories.
- Release belt tension using the manufacturer’s specified procedure.
- Remove the old belt.
- Compare the replacement belt with the original.
- Route the replacement belt around the correct pulleys.
- Restore the specified belt tension.
- Verify rib engagement and pulley alignment.
- Inspect the system before returning the engine to service.
Safety Warning: Never work around a running marine engine’s exposed belts, pulleys or rotating components. Follow the engine manufacturer’s service procedures.
Buy MerCruiser 57-8638763 Replacement Serpentine Belt at Pro Street Online
Maintain dependable marine engine accessory operation with the 57-8638763 MerCruiser V6/V8 Replacement Serpentine Belt.
Designed for select Alpha and Bravo engine configurations, this replacement belt is intended for applications specifying Mercury/MerCruiser 57-8638763 or its current equivalent, 865615Q03.
Find replacement belts and maintenance components at Pro Street Online.
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