Mercury – Plug | Cooling & Drain Port Seal | 97-8M0074531

Overview

If you’ve spent any time working on your own outboard, you know this plug plays a bigger role than its size suggests. When the old one starts getting worn, you’ll see a slow drip or feel it tighten with that scratchy, “not right” kind of bite. A good plug should thread in smooth and land with a clean, firm stop—that’s really all you’re looking for. Once it’s in, the cooling system stays sealed and you can get back to running the boat instead of chasing leaks.

Key Features

  • Durable Construction – Holds up to heat and vibration over regular use.
  • Accurate Thread Fit – Threads in straight and seats without much effort.
  • Corrosion-Resistant Material – Handles salt spray and damp storage fairly well.
  • OEM-Spec Seal Design – Gives the port a tight, steady seal.

Engine & Boat Compatibility

  • Mercury outboard cooling systems
  • Multi-cylinder engine platforms
  • Standard mechanical drain ports
  • Mercury service and maintenance series

Performance & Practical Benefits

A fresh plug helps the cooling system stay steady, which keeps the engine from drifting toward the warm side on longer runs. It also avoids those little air leaks that can make a motor act sluggish or inconsistent at idle. And when you pull it during service, it usually backs out clean instead of grabbing or tearing up the threads. It’s a small part, but it makes the rest of the job easier.

Why Buy OEM

The OEM plug matches the factory threads, and that alone saves a lot of frustration. Aftermarket versions can fit loose or corrode quicker, especially if you’re on the water a lot. Using the Mercury part just keeps everything simple and predictable.

FAQ

1. How do I know it’s time for a new plug?
If it doesn’t seat cleanly, leaks even when snugged down, or the head looks chewed up, it’s due.

2. Do I need sealant when installing it?
Most techs just use a tiny bit of marine-safe lube—nothing heavy.

3. How does it hold up in saltwater?
It does fine with normal rinsing and routine care.

4. Any tips for removing the old one?
Use the right-size tool and ease it out to keep the threads intact.

5. What happens if the plug is failing?
You might see small drips, warmer temps than usual, or a slow, uneven idle.