Mercury – Quicksilver 8M0174561 Thermostat Housing 140°F | Verado Cooling System | Composite & Stainless Steel | 8M0174561

Overview

If you’ve spent any real time on the water, you already know that an engine that runs cool and steady is an engine you can trust. There’s a calm that settles in when your temperatures stay right where they should — not climbing during long runs, not dipping when you idle into a quiet harbor. This 140-degree Mercury thermostat housing is one of those behind-the-scenes parts that keeps everything balanced. You may not think about it often, but when it’s doing its job, every minute on the water feels smoother, more predictable, and a whole lot more enjoyable.

Key Features

• Replacement 140°F thermostat housing for select Mercury 135–400 horsepower Verado 4-stroke outboards
• Built from corrosion-resistant, high-temperature composite material
• Integrated Stainless Steel thermostat for stable and accurate cooling control
• Molded housing includes a 90-degree outflow bend for proper routing
• Thermostat and housing included; seals, gaskets, clamps, and hardware sold separately

Engine & Boat Compatibility

Designed for:

• Mercury 135hp, 150hp, 175hp, 200hp, 250hp, 300hp, 350hp, and 400hp 4-stroke Verado outboards
• Common on offshore center consoles, bay boats, large pontoons, coastal cruisers, sport-fishing rigs, and high-power family boats
• Ideal for engines operating in demanding hot-weather or high-load environments

Performance & Practical Benefits

A thermostat housing may not be glamorous, but anyone who’s had temperature issues knows how important this component is. The 8M0174561 keeps coolant flowing at exactly the right pace, letting your Verado settle into that comfortable 140-degree sweet spot. When everything is aligned — the thermostat opening smoothly, the housing holding firm, and the flow path unobstructed — the engine feels tight, responsive, and steady.

You’ll notice how cleanly the engine holds temperature on long offshore runs, even when you’re pushing hard through heavy chop. At idle, the cooling system stays consistent, preventing heat fluctuations that can rob performance over time. The composite housing resists the corrosion that saltwater environments throw at it, while the internal Stainless Steel thermostat stays reliable season after season.

The installation itself is refreshingly straightforward. With basic tools and good access around the powerhead, most boat owners can handle it in their own driveway. Swap the old housing, replace the seals and clamps, tighten everything down, and you’re ready to go. The payoff is immediate — a cooling system that feels smoother and more balanced every time you hit the start button.

Why Buy OEM

Cooling components aren’t where you want to gamble on aftermarket shortcuts. Mercury designed this thermostat housing specifically for high-output Verado engines, which means the flow rate, temperature tolerance, and material stiffness are all exactly where they need to be. Aftermarket versions often miss the mark on internal tolerances or long-term heat resistance.

By choosing a genuine Mercury Marine part, you get perfect fitment, reliable operation, and long-term confidence. It’s one of those small investments that pays you back every time your engine runs cool, quiet, and right on temperature.

FAQ

Q1: Which Mercury engines does this thermostat housing fit?

It fits select Mercury Verado 135–400 horsepower 4-stroke outboards.

Q2: What makes this different from aftermarket housings?

OEM materials handle heat and corrosion better, and the internal Stainless Steel thermostat is calibrated precisely for Verado cooling systems.

Q3: How do I know it’s the correct replacement?

Match your engine model and horsepower range to the compatibility list, and confirm through your serial number.

Q4: Can this be used in both saltwater and freshwater?

Absolutely — the composite body and Stainless Steel thermostat are built for harsh marine environments.

Q5: Is installation straightforward?

Yes. With basic tools and proper seals and clamps, most boat owners can install it without difficulty.