EMP Ignition Coil 300-08309, Replaces Mercury 18-5186, Fits 15-20 HP Outboards

The EMP 300-08309 is a direct replacement ignition coil for Mercury outboard engines that originally used Mercury Marine part number 18-5186. The ignition coil is the component responsible for stepping up battery voltage into the high-voltage spark needed to fire the spark plugs, and a weak or failed coil is a common cause of hard starting, misfiring, or a no-spark condition on small outboards. This coil is built to match the fit, form, and function of the original 18-5186 unit so it installs in the same location using the same mounting points and wiring connections as the coil it replaces.

Coverage spans a range of Mercury outboard powerheads across the 15 HP, 15XD, 18 HP, and 20 HP families, including standard, Sea-Pro, Bullet, Commercial, and Non-Commercial model variants across multiple engine serial number ranges. Because Mercury revised coil part numbers at certain serial breakpoints, always confirm the serial number range for your specific outboard against the fitment list before ordering to make sure 18-5186 is the correct coil for your engine.

Specifications

• Brand: EMP
• Manufacturer Part Number: 300-08309
• Category: Mercury Outboard Ignition Coils
• UPC: 840080433806
• Weight: 0.439 pounds

Fitment

• Mercury 15 HP outboards, serial number ranges B292414-G760299, G760300 and up, and Sea-Pro serial range G044027-G437999
• Mercury 15 HP outboards, serial range G438000-G760299 and G760300 and up, including Commercial and Non-Commercial models
• Mercury 15XD outboards, Commercial and Non-Commercial models, serial range G760300 and up
• Mercury 18 HP outboards, serial range 5837437-6443972 and 6443973 and up, including Bullet Commercial models
• Mercury 20 HP outboards, serial ranges 3537531-3755884, 6443973-G044026, G044027-G437999, and G438000-G760299
• Mercury 20 HP Commercial and Non-Commercial outboards, serial range G760300-T800999

Replaces (OEM)

• Mercury Marine 18-5186

Frequently Asked Questions

What does the EMP 300-08309 ignition coil replace? It is a direct replacement for Mercury Marine ignition coil part number 18-5186, built to the same fit and function as that original part.

Which Mercury outboards does this ignition coil fit? The 300-08309 coil fits Mercury 15 HP, 15XD, 18 HP, and 20 HP outboards, including Sea-Pro, Bullet, Commercial, and Non-Commercial model variants, across the specific engine serial number ranges listed in the fitment chart.

How do I know if this coil is correct for my Mercury outboard's serial number? Mercury changed coil part numbers at certain serial number breakpoints, so match your outboard's engine serial number against the ranges listed for 15, 15XD, 18, and 20 HP models before ordering the 300-08309, which corresponds to Mercury part 18-5186.

How much does this ignition coil weigh? The EMP 300-08309 ignition coil weighs 0.439 pounds.

Is the EMP 300-08309 a genuine Mercury part or aftermarket? The 300-08309 is an aftermarket ignition coil manufactured by EMP as a replacement for Mercury Marine's 18-5186 coil, not an OEM Mercury part.

What symptoms indicate my outboard's ignition coil needs replacing? Hard starting, engine misfire, or a no-spark condition are common signs of a failing ignition coil, and replacing it with a coil like the EMP 300-08309 restores proper spark voltage to the plugs.

Does this coil fit the Mercury 15 HP Sea-Pro model? Yes, the 300-08309 covers the Mercury 15 HP Sea-Pro outboard within the serial number range G044027 to G437999.

Does this coil fit Commercial and Non-Commercial versions of the Mercury 20 HP? Yes, the 300-08309 fits both Commercial and Non-Commercial Mercury 20 HP outboards in the serial number range G760300 to T800999.

Does this coil fit the Mercury 18 HP Bullet model? Yes, the 300-08309 fits the Mercury 18 HP Bullet Commercial outboard for serial numbers 6443973 and up.

What is included when I order the EMP 300-08309? You receive one EMP 300-08309 ignition coil, the direct replacement for Mercury 18-5186.

Is installation of the 300-08309 coil straightforward? Because the EMP 300-08309 matches the original Mercury 18-5186 coil's mounting and wiring, it installs in the same location as the coil it replaces on covered Mercury 15, 15XD, 18, and 20 HP outboards.