FASWORX Outboard Thermostat & Housing Kit for Mercury Mariner 40–60hp — 110°F OEM-style replacement

FASWORX Outboard Thermostat & Housing Kit is a direct-fit replacement for Mercury Mariner 40–60hp 3-cylinder 2-stroke engines, restoring proper coolant flow with a 110°F thermostat element.

If your Mercury Mariner outboard is running hot, leaking around the thermostat housing, or you need a factory-style replacement after maintenance, this kit provides the thermostat and housing engineered to match OEM fitment. It replaces part numbers such as 850055A2, 850055A1, and 59078A2 and fits specified serial ranges for 40, 50, 55, and 60 horsepower models. The kit arrives ready to install, helping you avoid extended downtime and uncertain repairs.

Which Mercury Mariner engines will this thermostat kit fit?

This kit is designed for 3-cylinder 2-stroke Mercury Mariner outboards in the 40–60hp range within specified serial number windows. Confirm your engine’s serial number to ensure compatibility before ordering.

• 40 hp: USA serials 0G531301 and up; BEL serials 9855139 and up
• 50/55/60 hp: USA serials 0G590000 and up; BEL serials 9973100 and up
• Replaces OEM codes 850055A2, 850055A1, 59078A2

How does the 110°F thermostat affect engine performance?

The included 110°F (approximately 43°C) thermostat opens at a controlled temperature to allow coolant circulation, helping the engine reach and maintain optimal operating temperature. Proper thermostat function supports consistent engine warm-up and reduces the risk of overcooling or overheating in varied water conditions.

• 110°F opening point for balanced warm-up and cooling
• Precision spring and valve design for repeatable operation
• Helps stabilize running temperature under load and idle

What comes in the kit and is installation difficult?

The kit includes the thermostat element and the housing designed to mate with Mercury Mariner water jackets and hoses. Installation is straightforward for anyone familiar with outboard maintenance; basic tools and a clean gasket surface are all that's needed for a secure seal.

• Thermostat element sized for Mariner 3-cylinder 2-stroke engines
• Replacement housing molded to OEM shape and mounting points
• No special tools required—follow torque specs and gasket prep

How can I tell if my current thermostat or housing needs replacement?

Signs include inconsistent engine temperature gauge readings, visibly corroded or cracked housing, coolant leaks around the housing, or poor warm-up behavior. If the thermostat sticks closed or open, the engine may overheat or run too cool, both of which reduce efficiency and increase wear.

• Visible coolant leakage at the housing seams or gasket
• Engine takes too long to reach operating temperature
• Frequent temperature fluctuations under steady throttle

Who this kit is for: Boaters, marine technicians, and DIYers who own Mercury Mariner 40–60hp 3-cylinder 2-stroke outboards within the listed serial ranges and need a reliable, OEM-style thermostat and housing replacement. Choose FASWORX when you want a direct-fit part that replaces legacy numbers (850055A2, 850055A1, 59078A2) and helps restore correct coolant control quickly and confidently.