Mercury – ACDelco GM Original Equipment 41-983 Double Platinum Spark Plug | MerCruiser Big Block Ignition Series | Double Platinum Finish | 8M0129146

Overview

There’s a special kind of frustration when a big sterndrive engine doesn’t feel crisp. It might still run, but it doesn’t feel clean. Starts take a little longer, idle gets a touch rough, and you catch yourself listening harder than you should. Spark plugs are small parts with a big voice, and when they’re fresh and correct for the engine, you can feel the difference right away.

This Mercury Marine part is the plug you install when you want your MerCruiser to fire the way it was meant to. It’s steady, reliable, and built for the real rhythm of boating—long cruises, hot engine bays, and plenty of time under load. Put in the right plugs, and the whole boat feels calmer.

Key Features

• Double platinum spark plug designed for consistent ignition and long service life
• Built by ACDelco as a GM original equipment style plug
• Nickel alloy tip and copper core construction to support durability and dependable performance
• Ribbed suppressor seal design helps provide a secure seal and stable operation
• Recommended approach: replace spark plugs rather than cleaning used plugs
• Best practice: replace all engine plugs at the same time for balanced performance
• Fits applications including MerCruiser 496 MAG and 496 High Output, and MerCruiser inboard 8.1 liter and 8.1 liter High Output engines
• Mercury Marine part number 8M0129146

Engine & Boat Compatibility

• MerCruiser 496 MAG engines
• MerCruiser 496 High Output engines
• MerCruiser inboard 8.1 liter engines
• MerCruiser inboard 8.1 liter High Output engines
• Common on cruisers, performance runabouts, offshore-leaning sport boats, and larger family boats with big block power

Performance & Practical Benefits

Fresh spark plugs don’t just help the engine start—they help it run the way you remember. With the right plug in place, ignition tends to feel more consistent. Idle smooths out. Throttle response feels cleaner. You get that steady, confident pull when you ease into the power, instead of a slight hesitation that makes you second-guess the day.

The double platinum design is a practical choice for marine use because it’s built to hold up over time. Marine engines often spend long periods at a steady load, then shift into idle, then back to load again. That cycling can be hard on ignition components. A plug designed for durability helps keep performance stable, not just for the first trip after install, but across the season.

Installation is straightforward for most boat owners who are comfortable with routine maintenance. The key is being consistent: use the correct plug for your engine, gap it according to your manual, and swap the full set so everything is firing evenly. When you do it right, the engine feels tighter and more predictable, which is exactly what you want when you’re a long way from the ramp.

Why Buy OEM

Ignition parts are not the place to experiment. A genuine Mercury Marine part like this is chosen to match the engine’s needs—heat range, design, and overall fitment. That means fewer misfires, fewer weird running issues, and less time chasing problems that start with the wrong plug.

Aftermarket options can vary, even when they look similar on paper. OEM keeps it simple: install the plug your engine is designed to run, and you’ll get performance that feels right the first time. It’s practical advice, but it’s true—especially with big block MerCruiser power.

FAQ Section

Q1: Which Mercury engines or systems does the Double Platinum Spark Plug fit?

It’s intended for MerCruiser 496 MAG and 496 High Output, plus MerCruiser inboard 8.1 liter and 8.1 liter High Output engines. Always confirm with your engine owner’s manual.

Q2: What makes this part different from aftermarket alternatives?

It’s a Mercury Marine part built around GM original equipment style design with a double platinum configuration for consistent ignition and durability.

Q3: How do I know if this is the correct replacement for my setup?

Check your engine model and verify the recommended spark plug in your manual, then match the part number to 8M0129146.

Q4: Can this be used in both saltwater and freshwater applications?

Yes. Spark plugs serve the ignition system in any environment. Good maintenance and corrosion control habits help in saltwater.

Q5: Is installation straightforward for most boat owners?

For many owners, yes. Replace the full set, follow the manual for gap and torque, and you’ll usually feel a smoother, steadier engine right away.

• Supersessions
  33-863622, 33-881673, 33-8M0129146, 33-8M0129146