Mercury – NGK ITR4A-15 Laser Iridium Spark Plug | MerCruiser V6 & V8 Series | Iridium & Copper Core | 8M0204739

Overview

There’s nothing quite like that first turn of the key when the engine fires instantly — clean, sharp, and confident. It sets the tone for the entire day on the water. Whether you’re easing away from the dock or opening up the throttle across open chop, knowing your ignition system is rock-solid gives you peace of mind that’s hard to beat. This Mercury Marine part is built for that very feeling. With each spark delivering smooth, steady power, you’ll feel the difference long before you reach cruising speed.

Key Features

• NGK ITR4A-15 Laser Iridium spark plug designed for long-lasting, high-performance ignition
• Fine-wire Iridium center electrode for slow wear, stable idle, and crisp throttle response
• Copper core for efficient heat dissipation and consistent combustion
• Trivalent metal plating offers enhanced corrosion resistance in marine environments
• Ribbed suppressor seal prevents flashover and reduces misfires
• Mercury Marine part number 8M0204739
• Pre-gapped to manufacturer specifications

Engine & Boat Compatibility

• Fits select MerCruiser engines, including four-point-three-liter, five-liter, five-point-seven-liter, and six-point-two-liter models
• Suitable for sterndrive and inboard applications using NGK ITR4A-15 plugs
• Ideal for cruisers, sport boats, bowriders, cabin cruisers, and performance-oriented recreational boats
• Designed for engines where smooth idle, strong acceleration, and dependable ignition are essential

Performance & Practical Benefits

Ignition performance shapes how your entire day on the water feels. These Laser Iridium plugs deliver a tight, clean spark that keeps your MerCruiser running smooth from idle to wide-open throttle. The fine-wire Iridium tip requires less voltage to fire, which means more consistent combustion, improved fuel efficiency, and better throttle response — especially noticeable when accelerating hard or trimming the bow up in rough water.

The copper core draws heat away efficiently, reducing the chance of fouling during long idle sessions or frequent stop-and-go operation around marinas. You’ll notice the engine holds a steadier idle, responds with a smoother push, and maintains strong power across the full RPM range. And because of the high corrosion resistance of the trivalent plating, these plugs hold up well even in saltwater environments, making removal easier and more predictable after a full season of use.

Replacing the whole set restores uniform performance across all cylinders, giving your engine that balanced, “just-tuned” feel that makes the boat run tighter and cleaner than before.

Why Buy OEM

When you’re running a MerCruiser, the ignition system deserves nothing less than the engineering it was built around. Genuine Mercury Marine parts ensure the heat range, gap, electrode design, and materials match your engine exactly. Aftermarket plugs might resemble the real thing, but internal differences can lead to misfires, reduced power, or uneven wear — problems that only show up when you’re miles from the dock.

OEM plugs deliver consistent performance, longer life, and better protection against marine conditions. It’s the kind of practical advice any seasoned boater would offer: use the spark plugs Mercury intended, and your engine will reward you with smoother starts, cleaner performance, and fewer headaches.

FAQ

Q1: Which engines does the NGK ITR4A-15 Spark Plug 8M0204739 fit?

It fits select MerCruiser four-point-three-liter, five-liter, five-point-seven-liter, and six-point-two-liter engines.

Q2: What makes these spark plugs better than aftermarket versions?

The Laser Iridium tip, copper core, trivalent plating, and Mercury-approved specs offer superior durability, corrosion resistance, and consistent ignition.

Q3: How do I confirm it’s the right plug for my setup?

Check your owner’s manual or existing plug. If your engine calls for NGK ITR4A-15 or part number 8M0204739, you’re good to go.

Q4: Can these be used in both saltwater and freshwater boats?

Yes — the corrosion-resistant plating and ceramic insulator are built for all marine environments.

Q5: Is installation straightforward?

Absolutely. With a standard spark plug socket and careful threading, they install smoothly and seat securely.