Mercury – Thermostat | EFI FourStroke Cooling System | Marine Alloy | 8M0186873

Overview

When you spend your weekends chasing early light on quiet water or easing away from the dock with the family, you count on your engine to settle into that smooth, steady rhythm you know so well. A dependable thermostat is a small part, but it’s the reason your Mercury FourStroke warms up cleanly, runs efficiently, and never leaves you guessing. The Quicksilver 8M0186873 Thermostat gives you that peace of mind—the quiet confidence that your 25 or 30 horsepower Mercury EFI outboard is operating at the temperature it was engineered for. You feel it in the way the engine responds, the way it idles, the way the boat moves. Everything just feels right.

Key Features

• Helps maintain the proper engine operating temperature
• Designed specifically for Mercury 25hp and 30hp EFI FourStroke outboards
• Built to meet all Mercury Marine OEM specifications
• Durable construction for long, reliable service
• Thermostat only (hardware sold separately)
• Helps protect the engine from overheating or running too cool

Engine & Boat Compatibility

Ideal for a wide range of small-format boats that rely on smooth, responsive power:

• Mercury 25hp / 30hp EFI FourStroke outboards
• Serial number 1R154758 and higher
• Perfect for aluminum fishing boats, lightweight pontoons, inflatable dinghies, tenders, jon boats, and utility craft

If you run a boat where every ounce counts—and every horsepower matters—this thermostat is engineered for your setup.

Performance & Practical Benefits

You’ll notice the difference in everyday use. A healthy thermostat keeps temperature swings under control, which means:

• A tight, predictable warm-up instead of a sluggish one
• A smooth idle when you’re maneuvering around docks or shallow creeks
• Steady mid-range performance when you’re cruising along the shoreline
• Better fuel efficiency, thanks to proper engine temperature
• Long-term protection from overheating, warping, and internal wear

When your engine isn’t fighting temperature fluctuations, everything runs cleaner, quieter, and more confidently. It’s one of those maintenance upgrades you feel each time you turn the key.

Why Buy OEM

Think of OEM parts as the gear you choose when the stakes are real—not just convenient. With a genuine Mercury Marine part:

• Fitment is exact every time
• Materials meet strict Mercury engineering standards
• You get long-term reliability, not a short-term patch
• Installation is straightforward because everything lines up the way it should
• You avoid the hidden costs and hassles of bargain aftermarket substitutes

For many boaters, OEM is simply the smarter, more practical choice.

FAQ Section

Q1: Which Mercury engines does this thermostat fit?

It’s designed for Mercury EFI FourStroke 25hp and 30hp outboards with serial numbers 1R154758 and newer.

Q2: What makes this different from aftermarket thermostats?

OEM thermostats maintain precise temperature control and offer consistent performance, something aftermarket versions often can’t match.

Q3: How do I know if this is the correct replacement?

Check your serial number and confirm the part number in your engine’s owner or service manual.

Q4: Can this part be used in saltwater as well as freshwater?

Yes—Quicksilver parts are engineered to handle both environments when properly maintained.

Q5: Is installation straightforward?

Most boat owners with basic tools can replace a thermostat, though referencing your service manual is always recommended.