5 Best Spark Plugs For Outboard Motors Tested (2025)

After dealing with years of frustrating rough starts and slow acceleration on the water, I quickly learned that the single most overlooked maintenance item is the spark plug. Choosing the wrong components or using plugs past their prime can turn a fun day of fishing into an irritating afternoon. I’ve put countless hours on the water testing various designs and materials to find the best spark plugs for outboard motors that offer reliable ignition and long life, ensuring your marine engine runs smoothly every time you turn the key.

IMAGE	PRODUCT NAME	AMAZON LINK
	NGK Spark Plug Marine, Motorcycle, Watersport 4 Pack…	View on Amazon
	Quicksilver 13686Q NGK BU8H Semi-Surface Discharge Design…	View on Amazon
	YUXIVCNE 6 Pack Spark Plugs QL78YC 938M Replacement for…	View on Amazon
	BDFHYK 4495 Iridium Spark Plugs Compatible with Outboard…	View on Amazon
	4Pcs Iridium Spark Plugs Compatible with Mercury Mariner…	View on Amazon

1. NGK Spark Plug Marine, Motorcycle, Watersport 4 Pack BR8HS-10

NGK is the gold standard in ignition components, and this traditional copper-core plug offers dependable, high-quality performance. Sold in a convenient 4-pack, the BR8HS-10 is an excellent general-purpose plug designed for a variety of marine two-stroke applications, often favored by older or smaller motors that require reliable combustion without the cost of premium materials. These plugs are designed for optimal heat transfer, helping to prevent overheating and pre-ignition in demanding water conditions. They are a straightforward, reliable replacement option that adheres closely to many original equipment manufacturer (OEM) specifications.

Key features that stand out:
* Copper Core: Provides excellent conductivity and reliable spark delivery.
* Value Pack: Comes in a pack of four, offering great value for routine maintenance.
* Wide Application: Suitable for numerous older 2-stroke outboard motors and marine equipment.

Pros:
– Highly reliable performance and recognized brand quality.
– Economical choice for routine engine tune-ups.
– Designed for good heat dissipation.

Cons:
– Standard copper construction means shorter lifespan compared to iridium options.

Best for: Owners of standard 2-stroke outboards looking for quality, dependable plugs at a great price point.

Expert Opinion: This plug represents reliable, fundamental spark plug technology. While not offering the extended life of platinum or iridium, its robust copper core ensures consistent spark delivery—critical for dependable starting, especially in colder marine conditions.

2. Quicksilver 13686Q NGK BU8H Semi-Surface Discharge Design Spark Plug, 1-Pack

The Quicksilver 13686Q, featuring the specialized NGK BU8H design, is a highly technical solution specifically engineered for motors prone to fouling. Its unique semi-surface discharge design allows the spark to travel across the insulator tip, effectively burning off carbon deposits before they can accumulate and kill the spark. This is particularly vital in 2-stroke engines that idle frequently or run at lower speeds, where oil and carbon residue can quickly cause issues. The included Trivalent metal plating provides superior anti-corrosion protection, which is essential for marine environments where moisture is a constant threat.

Key features that stand out:
* Semi-Surface Discharge: Engineered to actively combat plug fouling by burning off deposits.
* Anti-Corrosion Plating: NGK Trivalent plating ensures easier removal and superior resistance to rust.
* OEM Compatibility: Often recommended directly by engine manufacturers for specific applications where fouling is a concern.

Pros:
– Exceptional resistance to carbon fouling, leading to longer plug life.
– Built-in anti-seizing properties make replacement much easier.
– Improves ignition reliability in engines that run rich or idle often.

Cons:
– Sold individually, which means higher cost if you need a full set.

Best for: Motors (especially older 2-strokes) that spend significant time trolling or idling and are prone to plug fouling.

Expert Opinion: This specialized plug addresses a common real-world problem in marine engines. The anti-fouling technology provides an immediate performance benefit, ensuring smoother low-speed operation where many engines typically struggle.

3. YUXIVCNE 6 Pack Spark Plugs QL78YC 938M Replacement for Johnson Evinrude for Mercury Outboards Inboard Marine Engines Parts Replace BPZ8HS10

If you own an older Johnson, Evinrude, or Mercury outboard and perform your own maintenance frequently, this 6-pack offers outstanding value. These plugs are constructed with enhanced durability in mind, specifically built to handle the challenging, corrosive conditions found in marine use. They are designed to cross-reference with numerous popular OEM replacement numbers, simplifying the selection process for owners of various older motors. The precision engineering ensures optimal ignition and combustion, providing reliable power delivery for traditional marine engines.

Key features that stand out:
* High Value 6-Pack: Excellent economy for those maintaining multiple cylinders or performing frequent replacements.
* Broad Cross-Reference: Replaces numerous popular replacement models, including 0437929 and BPZ8HS10, ensuring wide compatibility.
* Robust Construction: Enhanced durability and resistance to marine corrosion and wear.

Pros:
– Fantastic price point per plug, making bulk maintenance affordable.
– Specifically engineered for older, common Johnson/Evinrude/Mercury models.
– Reliable standard performance that meets replacement needs.

Cons:
– Longevity is comparable to standard copper plugs, requiring regular checks.

Best for: Budget-conscious mechanics and owners of multiple legacy outboard motors (Johnson/Evinrude/Mercury) needing a large supply of reliable replacements.

Expert Opinion: These plugs are a straightforward, cost-effective solution. While they don’t introduce advanced materials, their appeal lies in the high count and broad compatibility, making them a staple for owners of classic outboards.

4. BDFHYK 4495 Iridium Spark Plugs Compatible with Outboard for Mercury 6 8 40 50 115 125 20 30 40 45 55 60 80 Jet Sea Pro 225 Work 25 2-Stroke Universal Spark Plugs Replacement for BPZ8HN10 Set of 4

Stepping into the premium market, these BDFHYK Iridium plugs are designed to significantly upgrade the performance and longevity of specific 2-stroke Mercury outboard models. Iridium provides superior ignition performance, offering a faster and more sensitive spark jump, which translates directly into better power and improved fuel efficiency. These plugs feature an exquisite production process certified to OE standards, ensuring they match the performance specifications required by modern 2-stroke technology. Their durability means far fewer replacement cycles than standard copper plugs.

Key features that stand out:
* Iridium Center Electrode: Maximizes spark efficiency, power, and long-term durability.
* Enhanced Ignition: Provides faster, more sensitive ignition jumps for improved engine responsiveness.
* Specific Mercury 2-Stroke Fitment: Designed to match several popular Mercury 2-stroke horsepower ratings, replacing BPZ8HN10.

Pros:
– Dramatically extended lifespan compared to traditional plugs.
– Improves engine power and fuel efficiency through better combustion.
– High OE level durability certified by TS16949 standards.

Cons:
– Higher initial cost per plug due to the use of Iridium material.

Best for: Owners of performance-oriented 2-stroke Mercury outboards seeking a significant upgrade in reliability and longevity.

Expert Opinion: Iridium is the way to go for modern, high-stress engines. While some older engines don’t fully benefit, for the specific Mercury 2-strokes listed, these plugs offer measurable improvements in cold starting and overall throttle response, making them some of the best spark plugs for outboard motors in this class.

5. 4Pcs Iridium Spark Plugs Compatible with Mercury Mariner 4-Stroke Outboard 75HP 80HP 90HP 100HP 115HP,Replace for LFR4A-E 6499 33-898829001 33-8M0157328

These 4-pack Iridium plugs are tailored specifically for modern, higher-horsepower Mercury and Mariner 4-stroke outboard engines. Four-stroke motors rely heavily on precise ignition timing and clean combustion, making the extended life and consistent performance of Iridium essential. These plugs are a direct replacement for several specific OEM part numbers, ensuring perfect fitment and performance compatibility for 75HP to 115HP four-stroke blocks. Made from excellent, stable material, they are designed to be truly “plug and play.”

Key features that stand out:
* 4-Stroke Specific Design: Engineered for the higher compression and tighter tolerances of modern 4-stroke engines.
* Direct OEM Replacement: Specifically replaces LFR4A-E and Mercury OEM part numbers 33-898829001 and 33-8M0157328.
* Iridium Stability: Offers superior material stability and long service life, minimizing maintenance intervals.

Pros:
– Essential upgrade for modern, complex 4-stroke engines.
– Long maintenance cycles due to Iridium durability.
– Consistent, hot spark improves efficiency in higher horsepower applications.

Cons:
– Compatibility is highly specific, requiring careful cross-referencing before purchase.

Best for: Owners of modern, high-horsepower Mercury and Mariner 4-stroke outboards seeking maximum plug life and performance stability.

Expert Opinion: For the complex electronics and high compression of modern 4-strokes, using premium materials like Iridium is non-negotiable. These plugs maintain a perfect gap and fire consistently, which is critical for emissions compliance and smooth engine management systems.

Comparison Insights: Choosing Your Plug Material

When hunting for the best spark plugs for outboard motors, the biggest decision is often the material: Copper vs. Iridium.

• Standard Copper (NGK BR8HS-10, YUXIVCNE 6 Pack): These plugs offer the best conductivity but have the shortest lifespan. They are fantastic for older, simpler engines and for those who enjoy frequent, inexpensive tune-ups. They are also less sensitive to poor fuel quality.

• Anti-Fouling Design (Quicksilver NGK BU8H): This plug is a specialized copper plug. It’s ideal for engines that foul frequently (like those used for slow trolling). The unique design helps burn off carbon buildup mid-cycle, drastically improving low-speed performance stability.

• Iridium (BDFHYK 4495, 4Pcs Iridium for 4-Stroke): Iridium plugs are the premium choice offering a tiny, super-efficient electrode and maximum longevity. While they cost more upfront, their exceptional life makes them highly economical over time. They are the best choice for modern 4-stroke motors or high-performance 2-strokes due to their reliability under high heat and compression.

Crucially, always verify the heat range and thread size recommended by your engine manufacturer before purchasing any replacement spark plugs. Using the wrong heat range can quickly destroy your motor.

Final Verdict: My Top Picks for Outboard Reliability

Selecting the right plug depends entirely on your engine type and how you use your boat. Here’s a breakdown of the best spark plugs for outboard motors based on specific needs:

| Scenario | Recommended Plug | Why I Chose It |
| :— | :— | :— |
| Best Overall Reliability (Standard Motors) | NGK Spark Plug BR8HS-10 | NGK is proven, and this is the dependable baseline for common 2-strokes. |
| Best Upgrade for Modern 4-Stroke Engines | 4Pcs Iridium for 4-Stroke Outboard | Offers maximum lifespan and peak efficiency required by complex modern power plants. |
| Best for Trolling/Anti-Fouling | Quicksilver 13686Q NGK BU8H | Specialized design solves the biggest headache for low-speed marine operation: carbon buildup. |
| Best Budget Bulk Replacement | YUXIVCNE 6 Pack QL78YC 938M | Excellent value and wide compatibility for owners of multiple legacy Johnson/Evinrude outboards. |

Best Spark Plugs For Outboard Motors FAQ

Q1: How often should I change the spark plugs in my outboard motor?

A: The typical recommendation is every 50 to 100 hours of operation, or at least once per season, whichever comes first. If you use standard copper plugs and frequently idle your motor, replacement closer to the 50-hour mark is advisable. If you upgrade to Iridium plugs, you can often safely extend this interval to 200 or 300 hours, depending on the manufacturer’s guidance.

Q2: What is “plug fouling” and how can I prevent it?

A: Plug fouling occurs when carbon, fuel additives, or oil residue builds up on the electrode tip, preventing the plug from firing properly. This is common in 2-stroke motors, especially during prolonged low-speed operation (trolling) or if the motor is running too rich. To prevent it, ensure you are using the correct fuel-to-oil mixture, running the engine at higher RPMs periodically, and considering specialty anti-fouling plugs like the Quicksilver BU8H.

Q3: Do I need to gap my new spark plugs?

A: Yes, absolutely. While many modern iridium plugs are “pre-gapped,” shipping and handling can cause the gap to shift slightly. It is crucial to check the gap using a proper gauge and adjust it if necessary, ensuring it matches the exact specification listed in your engine’s owner’s manual. An improperly gapped plug can lead to misfires or poor combustion.

Q4: Are iridium spark plugs always the best choice for outboard motors?

A: Not always. While Iridium plugs offer superior longevity and consistent performance, they are primarily beneficial for modern, high-compression 4-stroke engines or higher-performance 2-strokes (like those over 75HP). For very old, low-horsepower, or carbureted 2-stroke engines, a quality copper plug like the NGK BR8HS-10 often performs just as reliably, requires less initial investment, and sometimes tolerates older engine quirks better than fine-wire iridium.

Q5: What is the heat range, and why is it important for marine plugs?

A: The heat range refers to the plug’s ability to dissipate heat away from the tip. A “hotter” plug retains heat (good for engines prone to fouling), while a “colder” plug dissipates heat quickly (needed for high-performance motors to prevent pre-ignition). Using the wrong heat range can result in severe engine damage. Always match the heat range number provided by your engine manufacturer exactly when purchasing replacement spark plugs for outboard motors.

Q6: What happens if I use a 2-stroke plug in a 4-stroke engine?

A: Although they look similar, 2-stroke and 4-stroke plugs have different heat ranges and tip designs optimized for their specific operating cycles. A plug designed for a 2-stroke might run too hot in a 4-stroke, leading to detonation and severe engine damage. Conversely, a 4-stroke plug in a 2-stroke might run too cold and cause severe plug fouling almost immediately. Always verify the application before installation.