NGK ITR4A15 Laser Iridium Spark Plug - 5599

NGK ITR4A15 Laser Iridium Spark Plug – 5599

The NGK ITR4A15 Laser Iridium Spark Plug, stock number 5599, is a premium ignition replacement for select MerCruiser MPI inboard and sterndrive engines. Designed for long service life and consistent firing performance, it combines a fine-wire iridium center electrode with a platinum-tipped ground electrode to provide dependable starting, smooth acceleration, and efficient combustion.

Marine engines regularly operate under sustained loads that place additional demands on the ignition system. The ITR4A15 is built to maintain a stable spark through repeated heat cycles while resisting electrode wear and gap erosion. NGK's copper-core construction also helps transfer heat away from the firing tip, while the resistor design reduces electrical interference with onboard electronics.

Replacing worn plugs can help correct hard starting, rough idle, hesitation, intermittent misfires, and declining engine performance. For compatible MerCruiser power packages, NGK 5599 is an excellent choice for scheduled maintenance or a complete ignition tune-up.

Spark Plug Specifications

• Manufacturer: NGK

• Part Number: ITR4A15

• NGK Stock Number: 5599

• Series: Laser Iridium

• Center Electrode: Fine-wire iridium

• Ground Electrode: Platinum-tipped

• Center Electrode Core: Copper

• Heat Range: 4

• Thread Size: M14 x 1.25

• Thread Reach: 17.5 mm

• Hex Size: 16 mm / 5/8"

• Seat Type: Tapered

• Spark Gap: 1.5 mm / .060"

• Resistor Type: Yes

• Sold Individually

Common MerCruiser Engine Applications

The NGK ITR4A15 / 5599 is used in select MerCruiser MPI and Tow Sports engines, including:

• MerCruiser 4.3L MPI V6

• MerCruiser 4.3L MPI EC

• MerCruiser 5.0L MPI V8

• MerCruiser 5.0L MPI EC

• MerCruiser 5.7L MPI

• MerCruiser 5.7L MPI MIE

• MerCruiser 5.7L MPI Tow Sports

• MerCruiser 5.7L MPI Tow Sports EC

• MerCruiser 350 MAG MPI

• MerCruiser 350 MAG MPI MIE

• MerCruiser 350 MAG MPI Horizon

• MerCruiser 377 MAG

• MerCruiser 377 MAG EC

• MerCruiser Black Scorpion Ski

• MerCruiser Black Scorpion Ski Gen+

• Select MerCruiser 6.2L MPI applications

Common Inboard & Tow Boat Applications

MerCruiser Tow Sports and Black Scorpion engines were installed in a variety of tournament ski, wake, and performance boats. Depending on model year and original engine package, potential applications include:

Centurion

• Centurion Avalanche

• Centurion Elite V

• Centurion Enzo SV230

• Centurion Enzo SV240

• Select Centurion Air Warrior models

Supreme

• Supreme V208

• Supreme V220

• Supreme V226

• Select Supreme wake boat models

Tige

• Tige 20V

• Tige 21i

• Tige 22V

• Tige 22Ve

• Tige 24V

• Tige 24Ve

Sanger

• Sanger V210

• Sanger V215

• Sanger V230

• Sanger DXII

• Select Sanger V-drive models

Common MerCruiser Sterndrive Boat Applications

The ITR4A15 is also used with compatible MerCruiser MPI sterndrive engines installed in recreational boats such as:

Sea Ray

• Sea Ray 185 Sport

• Sea Ray 205 Sport

• Sea Ray 210 Select

• Sea Ray 220 Sundeck

• Sea Ray 240 Sundeck

• Select Sea Ray Sundancer models

Chaparral

• Chaparral 204 SSi

• Chaparral 216 SSi

• Chaparral 226 SSi

• Chaparral 236 SSi

• Chaparral 246 SSi

• Select Chaparral Signature models

Crownline

• Crownline 202 BR

• Crownline 220 EX

• Crownline 240 EX

• Crownline 250 CR

• Crownline 270 CR

Four Winns

• Four Winns H200

• Four Winns H210

• Four Winns H220

• Four Winns H240

• Select Four Winns Vista models

Rinker

• Rinker Captiva 192

• Rinker Captiva 212

• Rinker Captiva 246

• Rinker 260 Express Cruiser

• Select Rinker Fiesta Vee models

Additional applications may include compatible MerCruiser-powered boats from Cobalt, Regal, Monterey, Stingray, Glastron, Larson, Formula, Baja, and other recreational boat manufacturers.

Mercury / MerCruiser Cross References

The NGK ITR4A15 / 5599 is associated with Mercury and MerCruiser replacement numbers including:

• Mercury / MerCruiser 8M0204739

• Mercury / MerCruiser 8M2018369

• Mercury / MerCruiser 884019

• Mercury / MerCruiser 884019001

• NGK ITR4A15

• NGK 5599

Key Features

• Genuine NGK ITR4A15 Laser Iridium spark plug

• NGK stock number 5599

• Designed for select MerCruiser MPI marine engines

• Fine-wire iridium center electrode provides excellent durability

• Platinum ground electrode helps minimize gap erosion

• Copper core promotes efficient heat dissipation

• Resistor construction helps reduce electrical interference

• Supports dependable starting and smooth acceleration

• Helps maintain efficient combustion under heavy engine loads

• Ideal for seasonal service and preventative maintenance

Premium Ignition Performance for MerCruiser MPI Engines

MerCruiser MPI engines depend on precise fuel and ignition control to deliver smooth power throughout the operating range. A worn spark plug can reduce ignition efficiency and contribute to misfires, difficult starting, hesitation, or reduced performance. The NGK ITR4A15 Laser Iridium design provides the durability and firing consistency needed for these electronically controlled marine engines.

Whether you're servicing a MerCruiser 4.3L MPI, 5.0L MPI, 5.7L MPI, 350 MAG MPI, 377 MAG, or Black Scorpion-powered boat, the NGK ITR4A15 Laser Iridium Spark Plug – 5599 provides a proven replacement for maintaining reliable performance on the water.

Fitment Note: MerCruiser used different spark plugs within the same engine displacement depending on model year, ignition system, emissions configuration, and serial-number range. Boat manufacturers also offered multiple engine packages in the same hull. Always verify NGK ITR4A15 / stock #5599 against your MerCruiser engine model, serial number, service manual, or original Mercury part number before ordering.