Best Marine Spark Plugs for Outboards and Other Watercraft

#1 · Best Overall

1. Champion 828M Copper Plugs

• Core Material: Copper
• Compatible with Vehicle Type: Car, Truck
• Thread Size: 14mm x 1.25
• Top Material Type: Metal

Best for: Four-plug copper-core replacement.

Why it ranks #1: A clearly labeled marine four-pack with copper core, 14 mm thread, 12.7 mm reach, and flat seat for checking against an engine manual.

A copper-core electrode is the defining feature of Champion’s four-pack, supporting conductivity and heat control while offering the wear characteristics specified for its small-engine plugs. The set also lists a 14 mm × 1.25 thread and solid terminal, giving buyers concrete details to compare with their engine’s requirements.

The copper core is specified to improve conductivity and heat control, which can help buyers seeking those characteristics in a marine replacement plug. Four plugs in the pack provide a set for replacement or spares, while the listed 14 mm × 1.25 thread, 12.7 mm reach, flat seat, and 21 mm hex help identify the installation dimensions. The listing advises checking the owner’s manual for the correct part number and installation, so those details should be matched before purchase.

Skip it if you need a surface-gap plug with stated carbon-fouling benefits; Quicksilver 13686Q lists that discharge design.

This four-plug Champion set suits owners whose manual specifies the listed QL77JC4 replacement and who want copper-core plugs for a marine small engine. Match the thread, reach, seat, and part number before installation.

Listed on Amazon as: Champion 828M Pack of 4 Copper Marine Spark Plugs (QL77JC4)

#2 · Best Outboard Pack

2. NGK 6431 BU8H Plugs

• Core Material: Copper
• Compatible with Vehicle Type: Watercraft
• Thread Size: M14 – 1.25

Best for: Six-plug Mercury and Mariner sets.

Why it ranks #2: This six-pack is specified for watercraft and lists compatibility with numerous Mariner and Mercury outboard models, plus copper-core construction.

A six-pack of NGK 6431 BU8H plugs is the central advantage for listed Mercury and Mariner outboard owners who need several plugs together. The product details name compatible engine families and identify a copper core and M14 × 1.25 thread for checking against the manual.

The six-plug quantity can serve an engine requiring multiple replacements or provide a matched supply of spares. Its listed compatibility covers named Mercury and Mariner outboard models, giving buyers specific model families to compare with their engine identification. The copper core and M14 × 1.25 thread add material and fit details, while the BU8H designation identifies the plug model. Match the exact engine and manual specification; the compatibility list does not make it universal across outboards.

Skip it if you need one plug with listed pregapped side electrodes and anti-seizing plating; Quicksilver 13686Q describes those features.

Choose this NGK six-pack when your Mercury or Mariner outboard appears in the listed compatibility range and calls for BU8H plugs. Its quantity suits multi-plug needs, but verify the precise model against the engine manual.

Listed on Amazon as: NGK 6431 BU8H Spark Plug – Fits Mariner Mercury Outboard (6 pack)

#3 · Surface-Gap Design

3. Quicksilver 13686Q BU8H

• Core Material: Copper
• Compatible with Vehicle Type: Watercraft
• Thread Size: M14x1.5
• Top Material Type: Metal

Best for: Surface-gap marine outboard use.

Why it ranks #3: A marine outboard plug with semi-surface discharge, copper core, anti-corrosion plating, and a stated recommendation to follow the engine manual.

Its semi-surface discharge design is the key differentiator: the listing says it improves ignition and burns off carbon before buildup can foul the plug. Quicksilver pairs that design with NGK construction, copper-core heat removal, and marine anti-corrosion and anti-seizing properties for outboard buyers.

Small side electrodes come pregapped, so this plug does not require gap adjustment, and the listing says the surface-gap design helps burn off carbon before it builds up. Copper core aids heat removal, while NGK Trivalent metal plating is specified for marine anti-corrosion and easier removal through anti-seizing. It is sold as one plug, making it a targeted replacement rather than a multi-plug supply. Quicksilver advises using only the plug specified in the engine manual.

Skip it if you need six plugs in one purchase for listed Mercury or Mariner models; NGK 6431 BU8H is sold as a six-pack.

This single Quicksilver plug fits buyers seeking the specified BU8H semi-surface design and its marine plating features. Use it only when the owner’s manual calls for this plug; the package quantity is one.

Listed on Amazon as: Quicksilver 13686Q NGK BU8H Semi-Surface Discharge Spark Plug for Marine Outboard Engines, 1 Pack

#4 · Largest Pack

4. ACDelco MR43LTS Eight-Pack

• Core Material: Copper
• Compatible with Vehicle Type: Watercraft
• Thread Size: 14mm
• Top Material Type: Ceramic

Best for: Eight-plug Mercury-family supply.

Why it ranks #4: The eight-pack is identified for Mercury Mercruiser Quicksilver applications and watercraft, with a copper core and 14 mm thread.

Eight plugs in one pack make this ACDelco MR43LTS listing a practical option when an application calls for several replacements or spares. Its title identifies compatibility with Mercury, Mercruiser, and Quicksilver, while the specifications list a copper core, ceramic top, and 14 mm thread for fit comparison.

The eight-pack supplies multiple MR43LTS plugs together, which can simplify stocking replacements when the engine application calls for this part. Its watercraft compatibility and the named Mercury, Mercruiser, and Quicksilver families help narrow the intended buying context. The listed copper core and ceramic top provide material details for comparison, and the 14 mm thread is an installation dimension to check against the engine manual. The listing does not provide further fit dimensions, so confirm the specified part before buying.

Skip it if you need stated reach, seat, and hex dimensions for comparison; Champion 828M lists those measurements.

Choose this ACDelco pack when the engine manual calls for MR43LTS and the named Mercury, Mercruiser, or Quicksilver fitment. Its eight-plug quantity suits stocking multiple replacements, but verify dimensions because reach and seat are not listed.

Listed on Amazon as: AC Delco OEM Part# 862029 MR43LTS Compatible With Mercury Mercruiser Quicksilver (8 Pack)

#5

5. ACDelco Gold MR43LTS

• Core Material: Copper
• Compatible with Vehicle Type: Watercraft
• Thread Size: Unspecified
• Top Material Type: Nickel

Best for: Single ACDelco marine replacement.

Why it ranks #5: This watercraft-specific single plug has a copper core, nickel-alloy tip, and ribbed suppressor seal; the listing advises using the manual's specified plug.

A nickel-alloy tip paired with a copper core distinguishes this single ACDelco MR43LTS marine plug. The listing also specifies a ribbed suppressor seal for durability and performance, giving buyers three construction details to assess when selecting a replacement for an engine that calls for this model.

The copper core and nickel-alloy tip identify the plug’s specified materials, while the ribbed suppressor seal is described as supporting durability and performance. One plug is included, so this listing suits an individual replacement or a small top-up rather than supplying an entire multi-plug set. ACDelco advises using the spark plug specified by the original equipment manufacturer and replacing all engine plugs at the same time; check the manual and plan quantity accordingly.

Skip it if you need four plugs in one purchase; Champion 828M supplies a four-pack with a copper core.

This ACDelco MR43LTS suits watercraft owners replacing a single plug or sourcing the specified model. Because it comes individually and the listing recommends replacing all engine plugs together, account for the engine’s full quantity.

Listed on Amazon as: ACDelco Gold MR43LTS (19355201) Marine Spark Plug

#6

6. Champion 821M L77JC4

• Core Material: Copper
• Compatible with Vehicle Type: Motorcycle
• Thread Size: 14 millimeters
• Top Material Type: Metal

Best for: Six-plug copper Champion set.

Why it ranks #6: A six-pack of copper marine plugs provides 14 mm thread, 12.7 mm reach, flat seat, and solid terminal, though compatibility should be verified.

Six copper-core Champion L77JC4 plugs give this pack a clear role for buyers needing several matching replacements. The listing specifies a 14 mm thread, 12.7 mm reach, flat seat, 21 mm hex, and solid terminal, offering useful dimensions to check against the engine’s required part.

A six-plug quantity can support replacing several plugs or keeping spares, provided the engine calls for this model. The copper core and metal top are listed materials, while the 14 mm thread and 12.7 mm reach help buyers check basic fit. The flat seat, 21 mm hex, and solid terminal add installation details. Champion advises consulting the owner’s manual for correct part identification and installation, so verify L77JC4 before using the set.

Skip it if you need six QL78YC plugs with a projected-tip configuration; MEILAN’s Champion replacement set lists that design.

This six-pack suits buyers whose equipment calls for Champion L77JC4 plugs and who want the listed copper-core construction. Although the title says marine, the specifications identify motorcycle compatibility, so verify application and dimensions in the manual.

Listed on Amazon as: Champion Copper Marine Spark Plug 821M L77JC4 Pack of 6

#7

7. MEILAN QL78YC Plugs

• Core Material: Copper or Nickel or Iridium
• Compatible with Vehicle Type: Watercraft
• Thread Size: 14 millimeters
• Top Material Type: Copper or Nickel or Iridium

Best for: Six projected-tip Champion plugs.

Why it ranks #7: This six-pack is identified for marine engines and watercraft, with a 14 mm thread and 12.7 mm reach; the listing urges compatibility checks.

A projected-tip configuration sets this six-pack of QL78YC plugs apart from standard non-projected options. The listing gives a 14 mm thread, 12.7 mm reach, flat seat, 21 mm hex, and solid terminal, helping buyers compare installation dimensions before choosing this Champion replacement set.

Six plugs provide a larger replacement supply for compatible marine engines, while the projected-tip configuration distinguishes the listed QL78YC model. Its stated 14 mm thread, 12.7 mm reach, flat seat, and 21 mm hex let buyers compare several physical requirements with the owner’s manual. The solid terminal is also specified. The listing explicitly advises checking the manual for the correct part number and installation, so the six-pack quantity does not replace application verification.

Skip it if you need copper-core conductivity and heat-control benefits expressly stated; Champion 828M describes those characteristics.

This six-pack suits buyers whose engine manual calls for Champion QL78YC plugs with a projected tip and the listed dimensions. Check the part number and fit before installation; the listing does not establish universal outboard compatibility.

Listed on Amazon as: SPARK PLUGS 6 PACK MARINE ENGINES 24 QL78YC 938M OUTBOARDS INBOARD I/O CHAMPION

#8

8. NGK BR8HS-10 Plugs

• Core Material: Nickel-alloy steel
• Compatible with Vehicle Type: Car, Truck
• Thread Size: 14mm
• Top Material Type: Ceramic

Best for: Four-pack NGK BR8HS-10 buyers.

Why it ranks #8: The four-pack explicitly mentions marine, motorcycle, and watersport use and provides a 14 mm thread, but lists car and truck vehicle compatibility.

The NGK BR8HS-10 comes as a four-pack, giving buyers a defined quantity for replacement or keeping spares on hand. Its listing identifies a 14 mm thread and nickel-alloy steel core, while the marine, motorcycle, and watersport title helps shoppers assess whether this model matches their equipment.

Four plugs in one listing can support a multi-plug replacement or provide spares, depending on the engine’s required count. The 14 mm thread offers a specific dimension to compare with the manual, and the nickel-alloy steel core identifies the listed core material. NGK names marine, motorcycle, and watersport uses in the title, but buyers still need to match the BR8HS-10 model to their engine rather than relying on broad category labels alone.

Skip it if you need a listed copper core and detailed reach and seat dimensions; Champion 828M provides those specifications.

This NGK four-pack suits owners whose manual specifies BR8HS-10 for marine, motorcycle, or watersport equipment. The thread and core material are listed, but check the complete plug dimensions and required model before fitting.

Listed on Amazon as: NGK Spark Plug Marine, Motorcycle, Watersport 4 Pack BR8HS-10

#9

9. TORCH E9Y-13 Plug

• Core Material: Ceramic
• Compatible with Vehicle Type: Boat
• Thread Size: 14mm x 19mm
• Top Material Type: Ceramic

Best for: Single TORCH marine replacement.

Why it ranks #9: The listing identifies boat compatibility and gives a 14 mm thread diameter and 19 mm thread length, but supplies only one plug.

The TORCH E9Y-13 listing specifies a 14 mm thread, 19 mm thread length, and 20.8 mm hex, making its dimensional details the clearest reason to consider this single marine plug. It also names Autolite 2852, NGK BUHW, and NGK BU8H in the title as reference applications.

The listed 14 mm diameter, 19 mm thread length, and 20.8 mm hex give buyers concrete measurements for comparison with their engine’s specified plug. The title also names Autolite 2852, NGK BUHW, and NGK BU8H, which can help identify intended cross-reference candidates, but manual verification remains important. One E9Y-13 plug is included, making it suitable for an individual replacement rather than a full set. Ceramic is listed as both core and top material.

Skip it if you need a six-pack with named Mercury and Mariner compatibility; NGK 6431 BU8H lists those engine families.

Consider this single TORCH plug when its E9Y-13 dimensions and named cross-references match the engine manual. The listing provides useful installation measurements, but one unit is supplied and fit should be confirmed before use.

Listed on Amazon as: TORCH E9Y-13 Marine Boat Spark Plug for Autolite 2852,NGK BUHW BU8H,1 PCS

#10

10. NGK 4838 BP8H-N-10

• Core Material: Nickel
• Compatible with Vehicle Type: Car, Truck
• Thread Size: 14 millimeters
• Top Material Type: Metal

Best for: Four-pack NGK V-groove plugs.

Why it ranks #10: This four-pack has a 14 mm thread, 12.7 mm reach, and 1 mm gap, but its listed vehicle compatibility is car and truck rather than watercraft.

NGK’s nickel tip with a V-groove is the defining feature of the BP8H-N-10 four-pack, while the listing describes standard plugs as constructed for longer life and optimum performance. A stated 1 mm gap and 14 mm thread give buyers measurable details for comparison.

Four BP8H-N-10 plugs provide a set or spare supply when this model is specified. The nickel V-groove tip identifies the electrode design, and the listed 1 mm gap lets buyers compare the plug’s gap specification with the engine manual. A 14 mm thread, 12.7 mm reach, gasket seat, and solid terminal add installation details. Match the exact model and dimensions before fitting; the listing’s broad vehicle categories do not establish fit for every marine engine.

Skip it if you need watercraft compatibility explicitly listed; ACDelco Gold MR43LTS identifies watercraft use.

This NGK four-pack suits buyers whose manual specifies BP8H-N-10 and who want the listed V-groove nickel design. Because the compatibility fields name cars and trucks, verify marine-engine application and exact fit before purchase.

Listed on Amazon as: NGK 4838 Pack of 4 Spark Plugs BP8H-N-10