Quicksilver – Idler Pulley | MerCruiser V8 Series | Flat 3.5-Inch Pulley | 865444T

Overview

There is a certain comfort in hearing your engine belt spin smoothly, with no chirps or chatter. When the belt system is right, you can feel it in the throttle response, the steering assist, even the way the boat settles into its cruise speed. If your idler pulley is worn, the whole engine starts to sound unsettled. This Mercury Marine part brings that quiet confidence back. It is a small component, but it plays a big role in keeping everything under the hatch running steady and dependable.

Key Features

• Replacement idler pulley for select MerCruiser V8 engines.
• Flat 3.5-inch pulley design.
• Built for serpentine belt systems.
• Marine-rated materials for corrosion resistance.
• Mercury Marine part number 865444T.

Engine & Boat Compatibility

• Fits MerCruiser V8 engines: 350, 377, and 496 cubic inch platforms.
• Suitable for 5.7L, 6.2L, and 8.1L V8 configurations.
• Commonly used in cruisers, performance boats, runabouts, bowriders, and offshore hulls.
• Performs well in both freshwater and saltwater boating.

Performance & Practical Benefits

Once installed, the pulley brings immediate stability to the belt path. The flat design works seamlessly with the serpentine belt, keeping it aligned as it wraps around multiple accessory components. You’ll notice the engine tone getting smoother, the vibration dropping slightly, and the accessories responding more predictably.

The pulley’s marine-rated construction protects it from moisture, heat, and the constant vibration of a marine engine compartment. The bearing spins with a steady, centered feel, eliminating the belt oscillation that creates noise and uneven wear. On longer runs, this stability translates into more reliable alternator output, consistent cooling-water flow, and a quieter ride overall.

Replacing the pulley is quick with basic tools, making it an easy upgrade during routine maintenance. Once the new pulley is in place, it feels like the entire belt system tightens up — not over-tensioned, just more controlled and secure.

Why Buy OEM

Idler pulleys depend on precision. If the grooves aren’t shaped correctly, or the bearing isn’t rated for marine heat, the pulley can fail early and take the belt with it. Aftermarket pulleys often cut corners in material hardness or bearing quality.

A Mercury Marine part avoids all those problems. The fitment is exact, the bearing is engineered for marine use, and the pulley runs true at all engine speeds. It’s the safest choice for long-term reliability.

FAQ

Q1: Which engines does this pulley fit?

It fits MerCruiser V8 engines: 350, 377, and 496 cubic inch models.

Q2: What makes this better than aftermarket pulleys?

Marine-rated bearings, exact sizing, and OEM durability.

Q3: How do I confirm it’s the right pulley?

Check your manual for pulley size. If you need a flat 3.5-inch pulley and the part number 865444T appears, this is correct.

Q4: Can it be used in saltwater?

Yes — the materials are resistant to corrosion.

Q5: Is installation straightforward?

Most boaters complete the job easily during belt replacement.