Best Spark Plugs For Mercury 4 Stroke Outboard

#1 · Best Overall

1. Rimzen Iridium LFR4A-E

• Core Material: Iridium
• Top Material Type: Iridium
• Compatible with Vehicle Type: Watercraft

Best for: 1.7L FourStroke iridium set.

Why it ranks #1: Explicitly fits Mercury and Mariner 75–115 HP 1.7L four-strokes, lists replacement numbers, and includes four plugs.

A high-purity iridium electrode with an ultra-fine design is the defining feature, which the listing connects to stronger ignition energy and stable spark output. The four-plug set specifically covers Mercury and Mariner 75–115 HP 4-Stroke engines, including stated 1.7L applications.

The listed fit includes 75, 80, 90, 100, and 115 FourStroke engines at 1.7L, plus 100 FourStroke BEL from 0P401000 onward. Replacement references LFR4A-E 6499, 33-8M0157328, and 33-898829001 help owners compare the existing plugs. The high-purity iridium and ultra-fine electrode are described as supporting stable ignition and complete fuel combustion. Four plugs are included, so the quantity suits a set replacement when the engine and references match.

Skip it if you have a Mercury 175–300 HP 4-Stroke; Promrmr LKAR7C-9 lists that higher-output engine range.

Owners of the specified Mercury or Mariner 75–115 HP 1.7L FourStroke engines can consider this iridium set when the replacement references match. The listed BEL cutoff is specific, so check the engine configuration rather than relying on horsepower alone.

Listed on Amazon as: Iridium Spark Plugs Replace LFR4A-E 6499 33-898829001 33-8M0157328, Fit for Mercury Mariner 4-Stroke Outboard 75HP 80HP 90HP 100HP 115HP-4Pcs

#2 · Best Listed Fitment Detail

2. atsuch Iridium LFR4A-E

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

Best for: 75–115 HP FourStroke replacement.

Why it ranks #2: Names the same 75–115 HP 1.7L four-stroke range and 100 HP BEL serial detail, with four plugs and a one-year warranty.

A four-plug iridium set specifies Mercury and Mariner 4-Stroke compatibility across 75–115 HP, including 1.7L engines. That stated range gives owners a focused replacement option, while the listed equivalent part numbers help identify it against an existing plug before installation.

The listing names LFR4A-E 6499, 33-898829001, and 33-8M0157328, so buyers can compare those identifiers with the plugs being replaced. Its stated fit includes 75, 80, 90, 100, and 115 FourStroke engines, plus 100 FourStroke BEL from 0P401000 onward. Iridium core and top material are specified, and the four-plug package suits a complete set replacement. The listing describes installation as easy and plug-and-play, but still calls for checking the replacement-part model.

Skip it if you have a 175–300 HP Mercury 4-Stroke; Promrmr LKAR7C-9 lists that higher-output range.

Mercury or Mariner 4-Stroke owners within the stated 75–115 HP and 1.7L range can consider this four-plug iridium set. Check the engine configuration and replacement identifiers, especially for the listed 100 FourStroke BEL cutoff.

Listed on Amazon as: 4Pc Iridium Spark Plugs LFR4A-E 6499 Fit Mercury 4-Stroke Outboard 75-115HP

#3 · Best for 75–115 HP Range

3. GUQVKI Iridium Plugs

• Core Material: Iridium
• Top Material Type: Iridium
• Compatible with Vehicle Type: Watercraft

Best for: Cold-start ignition priority.

Why it ranks #3: Its title specifies Mercury and Mariner 4-stroke outboards from 75 to 115 HP, and the replacement number is 33-8M0157328.

Iridium electrodes are the defining feature here, with the listing linking them to concentrated, stable ignition and easier starts in cold or damp conditions. Mercury and Mariner 4-Stroke owners in the 75–115 HP range get a stated application alongside those ignition-focused claims.

The product identifies Mercury and Mariner 4-Stroke outboards from 75 to 115 HP, giving buyers a defined power range to compare with their engine. Its iridium material is described as resistant to high temperatures and wear, while the listing says the ignition process uses energy efficiently and can help in cold, damp environments. Those details may matter to owners prioritizing starting behavior, but the supplied listing does not state a plug count or specify additional engine configurations.

Skip it if you need a stated four-plug package and 1.7L application; atsuch LFR4A-E 6499 lists both details.

This suits Mercury or Mariner 4-Stroke owners in the listed 75–115 HP range who value the stated cold-start and damp-condition ignition benefits. The listing leaves package quantity and exact engine configurations unspecified, so those details may determine suitability.

Listed on Amazon as: Iridium Spark Plugs Fit for Mercury Mariner 4-Stroke Outboard 75HP-115HP

#4 · Best for Higher-Horsepower Models

4. Promrmr LKAR7C-9

• Core Material: Iridium
• Top Material Type: Iridium
• Compatible with Vehicle Type: Watercraft

Best for: High-output V6 and V8 outboards.

Why it ranks #4: Lists Mercury four-stroke outboards from 175 to 300 HP and 450R V6 and V8 models, with four plugs and a one-year warranty.

Compatibility with Mercury 175–300 HP outboards and 450R models is the defining point of this four-plug iridium set. Its stated coverage includes 3.4L V6 and 4.6L V8 4-Stroke engines, giving higher-output owners a specific application range to check.

The product lists LKAR7C-9 and 93961 alongside replacement references 8M0135348 and 33-8M0135348, helping identify the intended plug. Its fit text names Mercury outboards from 175 through 300 HP and 450R 3.4L V6 and 4.6L V8 4-Stroke models. Iridium is specified for the core and top material, and four plugs are included. This application focus makes it distinct from lower-rated 75–115 HP sets, but the exact model and replacement reference still need to match.

Skip it if you run a 75–115 HP Mercury 4-Stroke; Rimzen LFR4A-E 6499 lists that lower-output range.

This set is aimed at Mercury owners with the listed 175–300 HP or 450R 4-Stroke applications who need four iridium plugs. Use the model and replacement references as boundaries; the listing does not establish fit for lower-output engines.

Listed on Amazon as: Set of 4 Iridium Spark Plugs LKAR7C-9 93961 Compatible with Mercury Outboard Motor 175 HP Through 300 HP 450R V6 V8 4.6L 4-Stroke Outboards Replace 8M0135348 33-8M0135348

#5

5. NGK Laser Iridium ILFR6GE

• Core Material: Iridium
• Top Material Type: Metal
• Compatible with Vehicle Type: Watercraft
• Thread Size: 14mm x 1.25mm

Best for: Marine OEM-spec iridium set.

Why it ranks #5: The listing says this four-pack meets Mercury Marine OEM specifications and describes marine corrosion protection, but does not state an engine range.

Laser iridium construction paired with trivalent metal plating is the defining combination, with the listing tying the plating to marine corrosion resistance. This four-plug NGK set also states Mercury Marine OEM specifications, a useful reference for owners whose manual calls for ILFR6GE 4212.

The pre-gapped design is described as matching the engine manufacturer’s specification, which can simplify installation when this is the prescribed plug. Iridium material and trivalent plating are presented as durability and marine corrosion benefits, while the copper core and ribbed suppressor seal are linked to durability and performance. The four-pack supports a set replacement. The listing does not provide a Mercury horsepower range, so OEM-spec language should not replace checking the engine manual for the exact application.

Skip it if you need a named 75–115 HP engine range; atsuch LFR4A-E 6499 lists specific Mercury 4-Stroke ratings.

Mercury owners whose manuals call for ILFR6GE 4212 can consider this four-plug iridium set for its stated marine plating and pre-gapped design. The listing gives no engine range, so the precise model specification remains the deciding boundary.

Listed on Amazon as: Boating Accessories New NGK Laser Iridium Spark Plug ILFR6GE, 4212 Set of 4 Spark Plugs

#6

6. SYKRSS Iridium 4838

• Core Material: Iridium
• Top Material Type: iridium
• Compatible with Vehicle Type: Watercraft
• Thread Size: RM

Best for: Broad Mercury rating coverage.

Why it ranks #6: Lists a broad Mercury horsepower range and four plugs, but its supplied fitment does not establish that the covered engines are four-stroke.

This four-pack lists Mercury and Mariner applications from 6 to 125 HP, including several small and midrange ratings. Its iridium plugs replace 4838 and BP8H-N-10, giving owners those concrete references to check while considering a wide range of outboard applications.

The specified rating list includes 115, 100, 80, 60, 40, 25, 20, 9.9, and 6 HP, among other Mercury and Mariner engines. That breadth makes the stated compatibility useful for owners whose rating appears in the listing, though it does not itself establish every engine configuration. Iridium core and top material are specified, and the OE replacement references are 4838 and BP8H-N-10. The four-pack supports set replacement; thread size is listed as RM and gap as 1 mm.

Skip it if you need an explicitly stated 4-Stroke application and M14x1.5 thread; atsuch LFR4A-E 6499 supplies both details.

Mercury or Mariner owners whose rating and replacement reference match the listing can consider this four-pack for a set change. Its broad HP list does not specify engine cycles, so verify that the exact application matches before relying on it for a 4-Stroke.

Listed on Amazon as: Iridium Spark Plug 4838 4 Pack for Mercury Outboard

#7

7. Quicksilver NGK BU8H

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

Best for: Marine corrosion-conscious replacement.

Why it ranks #7: Quicksilver states its products match Mercury Marine OEM performance specifications, but the listing does not give a four-stroke engine range and includes one plug.

A semi-surface discharge design is the key differentiator, with the listing saying it burns off carbon before buildup can foul the plug. This single Quicksilver NGK BU8H also uses marine-oriented trivalent plating, making it a considered option when corrosion resistance matters.

The semi-surface discharge design and small side electrodes are described as helping manage carbon without requiring gap adjustment; the plug is also said to be nearly immune to pre-ignition. Trivalent metal plating provides stated anti-corrosion and anti-seizing benefits in marine use, while a copper core aids heat removal. Quicksilver says its products match Mercury Marine OEM performance specifications. It is sold as one plug, and the manufacturer explicitly advises using only the plug specified in the engine manual.

Skip it if you need four plugs in one package; NGK BP8HS-15 6729 is listed as a four-pack.

Choose this single Quicksilver BU8H when the engine manual specifies that plug and marine corrosion protection is a priority. Its one-plug package suits individual replacement better than a full set, and the manual remains the fit authority.

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

#8

8. NGK BP8HS-15

• Core Material: Copper
• Top Material Type: Nickel
• Compatible with Vehicle Type: Watercraft, all-terrain-vehicles…
• Thread Size: 14mm x 1.25mm

Best for: Copper-core marine standard plug.

Why it ranks #8: The four-pack listing identifies a standard plug and recommends checking the manual, but does not specify Mercury four-stroke fitment.

A solid copper core paired with a nickel-tipped electrode defines this four-pack, while the listing also claims resistance to carbon buildup and pre-ignition. The product is identified as NGK 6729 BP8HS-15, with watercraft among its specified vehicle types.

The stated heat-range operation, carbon-buildup resistance, and pre-ignition resistance offer practical reasons to consider this standard plug when its application matches. High-alumina ceramics are described as supporting heat transfer and electrical insulation, and a triple-gasket seal is said to prevent combustion-gas leakage. Four plugs are included and the description says each comes pre-gapped to 1.5 mm, while recommending a gap check before installation. Use only the plug specified by the engine manual.

Skip it if you want an explicitly listed 75–115 HP Mercury 4-Stroke application; Rimzen LFR4A-E 6499 names that range.

This NGK standard four-pack suits buyers matching the 6729 BP8HS-15 reference and seeking the listed copper-core and sealing features. Since no Mercury 4-Stroke range is supplied, let the engine manual—not the broad watercraft category—determine fit.

Listed on Amazon as: NGK 6729 Spark Plug – BP8HS-15, 4 Pack

#9

9. NGK BP8HS15

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

Best for: Four-plug NGK standard set.

Why it ranks #9: This genuine NGK four-pack lists a 14 mm thread, but its stated vehicle types and fitment details do not establish Mercury four-stroke compatibility.

A genuine NGK standard 6729 four-pack is the concrete appeal here, providing four copper-core, nickel-top plugs for a set replacement. The supplied information identifies it as a direct replacement part, but its vehicle-type specifications list cars and trucks rather than watercraft.

The four-plug package can serve a complete set change where the BP8HS15 6729 reference is the correct match. Its copper core and nickel top material identify the specified construction, while NGK branding and the direct-replacement description provide useful product references. However, the specifications list car and truck compatibility, not watercraft, and provide no Mercury 4-Stroke application range. That makes this a cautious choice for an outboard roundup: the engine manual must explicitly call for this plug before purchase.

Skip it if you require listed Mercury marine fit; Quicksilver 13686Q explicitly identifies marine outboard engines.

Consider this NGK four-pack only when the engine documentation identifies 6729 or BP8HS15 as the correct plug. Its supplied vehicle compatibility is car and truck, so Mercury 4-Stroke owners should not infer marine fit from the product title alone.

Listed on Amazon as: NGK New Standard Spark Plug BP8HS15, 6729 Set of 4 Spark Plugs

#10

10. BDFHYK Iridium 4495

• Core Material: Iridium
• Top Material Type: Iridium
• Compatible with Vehicle Type: Watercraft
• Thread Size: 20.4mm

Best for: Broad Mercury plug cross-reference.

Why it ranks #10: Its compatibility details primarily describe Mercury two-stroke models, so it is the weakest match for a four-stroke-focused search.

A compatibility list spanning many Mercury engine ratings is the defining feature of this four-pack, but it explicitly includes 2-Stroke applications. That broad range may help owners matching the 4495 or BPZ8HN10 reference, while making engine-cycle verification especially important for a 4-Stroke roundup.

The listing identifies replacement 4495 and BPZ8HN10 and names numerous Mercury ratings, including 6, 8, 40, 50, 115, and 125, while specifying 2-Stroke in its compatibility text. Its iridium material and claimed sensitive ignition response are presented as support for ignition performance. A four-pack is included, with a stated 1 mm gap and 20.4 mm thread size. Because the supplied fit details point to 2-Stroke engines, this is not an assumed match for Mercury 4-Stroke owners.

Skip it if you own a 4-Stroke and need an explicitly listed application; atsuch LFR4A-E 6499 states Mercury 4-Stroke fit.

Mercury owners matching the listed 4495 or BPZ8HN10 references may find the broad ratings and four-pack relevant, particularly for the stated 2-Stroke applications. Do not treat its extensive engine list as proof of 4-Stroke compatibility.

Listed on Amazon as: BDFHYK 4 Pack Iridium Spark Plugs Replacement for 4495 BPZ8HN10