Boating Accessories NGK Laser Iridium Spark Plug Set IZFR5G (5887) – Set of 4, Pre-Gapped for Mercury OPTIMAX 135–250

NGK Laser Iridium IZFR5G (5887) spark plug set of 4 is a high-durability ignition component engineered for select Mercury OPTIMAX outboards (models 135–250) to restore reliable starting and consistent combustion.

This four-pack of NGK IZFR5G spark plugs (OEM reference 889597001) is designed for mid- to high-powered Mercury OPTIMAX engines—covering 135, 150, 175, 200, 225 and 250 models. Each plug features an iridium-tipped center electrode for extended life, a nickel construction for robust corrosion resistance, and comes pre-gapped to the recommended specification to simplify installation. The plugs aim to deliver steady ignitability and lasting performance in marine environments where salt, vibration, and heat are persistent challenges.

How will these spark plugs affect engine starting and throttle response?

Replacing worn plugs with new IGFR5G iridium tips improves spark consistency, which helps the engine fire more reliably at cranking and under load. That translates to quicker starts, smoother idling, and more predictable throttle response when underway.

• Iridium center electrode for strong, stable spark
• Pre-gapped for correct firing distance out of the box
• Reduced misfires during acceleration and load changes

Are these NGK plugs compatible with my Mercury OPTIMAX outboard?

These IZFR5G plugs match the OEM specifications used in many Mercury OPTIMAX four-stroke and two-stroke direct-injection models in the 135–250 hp range. Always verify part numbers against your engine manual or existing plugs to confirm fitment before purchase.

• OEM reference: 889597001 compatible with specified OPTIMAX models
• Set of 4 covers full-bank replacement on most applications
• Pre-gapped to manufacturer recommendations for quick swap

What materials and features ensure durability in saltwater use?

The plugs use a nickel body combined with a laser-welded iridium tip for a balance of corrosion resistance and electrode longevity. These materials resist electrode erosion, while the construction minimizes the effects of vibration and thermal cycling common in marine engines.

• Nickel body resists external corrosion
• Iridium tip extends service life over standard plugs
• Factory pre-gapping maintains proper spark gap over time

What should I expect during installation and maintenance?

Installation is straightforward: remove the old plugs, check threads and sealing surfaces, and install the new NGK IZFR5G plugs to the torque specified by Mercury. Because these come pre-gapped, you only need to verify gap and torque rather than adjust the electrode spacing.

• Sold as a set of 4 for full-bank replacement
• Pre-gapped—verify gap and torque to OEM specs
• Inspect spark plug wells and boot seals while changing

Who is this for: Boaters, marine technicians, and DIY enthusiasts who own Mercury OPTIMAX-powered boats (135–250 hp) and want a durable, OEM-compatible spark plug upgrade. This NGK Laser Iridium IZFR5G set is best for those seeking longer service intervals, reliable ignition in variable marine conditions, and a plug that installs quickly without gap adjustments. Verify your engine’s part number before ordering to ensure proper fitment.