Quicksilver – Idler Pulley | MerCruiser V6 & V8 Series | 6-Groove Pulley Design | 864625T

Overview

Every boater knows the importance of a quiet, well-behaved serpentine belt system. When the belt tracks straight, tensions properly, and runs over smooth pulleys, the whole engine feels calmer. But when an idler pulley starts to go, you hear it — that faint chirp, that slight vibration, that little reminder that it’s time for fresh hardware. This Mercury Marine part replaces that uncertainty with confidence. It’s a simple component, but one that keeps everything else moving the right way.

Key Features

• Replacement idler pulley for MerCruiser V6 and V8 engines
• Six-groove, 4.25-inch diameter design
• Built for engines using serpentine belt systems
• Marine-grade materials for long-term durability
• Mercury Marine part number 864625T

Engine & Boat Compatibility

• Fits MerCruiser V6 and V8 engines from 1998 and newer
• Compatible with 305, 350, and 377 cubic inch platforms
• Found on cruisers, sport boats, runabouts, bowriders, and many family performance boats
• Designed for both freshwater and coastal operation

Performance & Practical Benefits

You’ll feel the difference this pulley makes the moment the engine starts. The belt glides over it with a smooth, centered motion, eliminating the chatter or wobble caused by a worn or aging pulley. That tight tracking improves the performance of everything the belt drives — alternator, water pump, power steering, and more.

The pulley rotates cleanly on its bearing, producing a steady, controlled feel that helps reduce belt wear and engine vibration. The grooves are machined precisely to match MerCruiser belt profiles, so alignment is crisp and predictable. This level of accuracy matters at higher RPMs, where even slight misalignment can cause heat, noise, or premature bearing wear.

Installation is straightforward using common tools. Once installed, the pulley gives you that small but meaningful feeling of mechanical confidence — the sense that your belt system is back to factory-smooth operation.

Why Buy OEM

Aftermarket pulleys often miss the groove spacing, bearing quality, or material hardness required for marine applications. A pulley that works fine on paper can fail quickly under the heat and vibration of a real engine compartment.

A genuine Mercury Marine part avoids those problems entirely. It’s engineered for the exact load, speed, and environment your engine operates in. It lasts longer, spins truer, and protects your belt and accessories from unnecessary wear. It’s the kind of part seasoned boaters choose because it saves time, money, and frustration.

FAQ

Q1: Which engines does this idler pulley fit?

It fits MerCruiser V6 and V8 engines from 1998 and newer using serpentine belt systems.

Q2: How is this different from aftermarket pulleys?

Precision groove alignment, higher bearing quality, and marine-rated construction.

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

Check your engine manual — if it calls for a six-groove, 4.25-inch pulley and lists part 864625T, this is correct.

Q4: Can it be used in saltwater?

Yes — the materials are built for both environments.

Q5: Is installation simple?

Most boaters can install it with basic hand tools.