Mercury – Serpentine Belt | Engine Drive System | Rubber Composite | 865615Q09

Overview

Every boater knows that the simplest parts often make the biggest difference. A serpentine belt isn’t flashy, but when it’s doing its job, you feel it in every smooth shift of the throttle and each steady hum from your alternator. Engines from this era—especially early Alpha-series V6 and V8 models—tend to tell you right away when something is off. That’s why using a belt you trust matters. With this Mercury Marine part, you get that quiet, steady confidence that your boat will behave exactly the way you expect as you push away from the dock or glide back in after a long run.

Key Features

• Designed for 1999–2001 MerCruiser V6 and V8 Alpha engines.
• Fits 305 and 350 cubic inch configurations.
• Built for high-mounted alternator applications.
• Marine-grade rubber composite for durability.
• Exact replacement for the original factory belt.
• Engineered to maintain smooth tension, accurate tracking, and long service life.

Engine & Boat Compatibility

• Fits 1999–2001 MerCruiser V6 and V8 (305 & 350 cubic inch) Alpha engines.
• Compatible with engines in serial range 0L619000–0M320024.
• Designed specifically for high-mounted alternator configurations.
• Used on runabouts, family cruisers, older sport boats, and multi-purpose recreational vessels.
• Suitable for both sterndrive and inboard layouts using this exact routing pattern.

Performance & Practical Benefits

When this belt is installed, your engine regains the smoothness it may have been missing. The right serpentine belt keeps the cooling system moving steadily, helps the alternator charge efficiently, and ensures your accessories run with a balanced load. Instead of squeaks, slips, or tension problems, everything feels tight, predictable, and well-synchronized.

One of the biggest advantages of using an OEM belt is how naturally it fits during installation. With aftermarket belts, you often end up wrestling with tension or dealing with small inconsistencies in length. This Mercury Marine part slots into the pulleys cleanly, finding its tension point exactly where the engine was designed to hold it. That correct alignment helps reduce glazing, overheating, and premature failures—issues that can quickly ripple into bigger engine problems.

Built from a rubber compound specifically engineered for marine heat cycles, long run times, and constant exposure to humidity, this belt handles real-world conditions without breaking down early. For older engines still putting in regular hours, that durability keeps you on the water and out of the shop.

Why Buy OEM

These engines rely heavily on proper accessory load management, and small differences in belt length or material quality can have big effects. Choosing an OEM serpentine belt ensures everything fits, aligns, and performs exactly as Mercury intended. You’re not gambling with generic materials or close-enough sizing. Instead, you’re choosing the belt that your engine would have left the factory with. If another boater asked what to use, this is the belt you’d recommend every time.

FAQ Section

Q1: Which engines does this belt fit?

It fits 1999–2001 MerCruiser V6 and V8 Alpha engines with high-mounted alternators.

Q2: What makes this different from aftermarket options?

It matches factory specifications exactly, ensuring smooth engagement, proper tension, and long-term durability.

Q3: How do I know this is the correct part?

Check your engine model, confirm a high-mounted alternator, and verify your serial range falls between 0L619000 and 0M320024.

Q4: Can this belt be used in saltwater and freshwater?

Yes, it's built from marine-rated materials made for both environments.

Q5: Is installation straightforward?

Most boaters can install it with basic tools and the engine’s routing diagram.