F.S.P Thermostat Kit for Mercury Mariner 3-Cylinder 40–60 HP — Direct-Fit OEM Replacement

F.S.P's thermostat kit is a direct replacement thermostat assembly designed to restore proper engine cooling for Mercury Mariner 3-cylinder 2-stroke outboards (40–60 HP) using part numbers 59078A2, 13141, and 850055A2.

This replacement kit fits a range of Mercury Mariner GLM 110 3-cylinder 2-stroke engines (40, 50, 55, 60 HP) and is engineered to match OEM fit and function. It’s supplied as a single, complete thermostat kit and cross-references common Mercury part numbers so you can replace the failing thermostat quickly and avoid overheating or inefficient engine warm-up caused by a faulty unit.

Which Mercury engines and serial ranges does this thermostat kit fit?

This F.S.P kit is specifically listed for 3-cylinder 2-stroke Mercury Mariner engines in the 40–60 HP range. Fitment varies by horsepower and origin (USA/BEL) and is set by serial number ranges to ensure compatibility.

• 40 HP: USA serial 0G531301 & up, BEL 9973100 & up
• 50, 55, 60 HP: USA serial 0G590000 & up, BEL 9973100 & up
• Cross-replaces Mercury part numbers 850055A2, 850055A1, 59078A2, 13141

What does the kit include and how does it replace the original part?

The package contains one complete thermostat kit designed to replace the listed Mercury part numbers. The components are sized and shaped to install in the factory thermostat housing without modification, restoring correct coolant flow control.

• One thermostat kit per box, ready for installation
• Direct-fit components matched to OEM dimensions and seals
• No additional gaskets or machining typically required

How will installing this thermostat kit affect engine performance?

A correctly operating thermostat helps the engine reach and maintain optimal operating temperature faster and keeps temperature steady under load. Replacing a sticking or failed thermostat can reduce warm-up time and prevent overheating, improving fuel efficiency and protecting engine components.

• Helps maintain steady coolant temperature during operation
• Reduces risk of overheating from a stuck-closed thermostat
• Supports proper thermally controlled engine timing and performance

How difficult is installation and what should I check before buying?

Installation is typically straightforward for anyone comfortable with basic outboard service; it requires access to the thermostat housing and simple hand tools. Before purchasing, verify your engine model and serial number against the listed fitment to ensure compatibility and inspect the housing for corrosion that might require additional parts.

• Basic mechanic skills and standard tools usually sufficient
• Confirm engine model and serial number match fitment ranges
• Inspect thermostat housing and surrounding seals for wear

Who is this for: This F.S.P thermostat kit is intended for boat owners, marine mechanics, and service shops maintaining Mercury Mariner GLM 110 3-cylinder 2-stroke outboards (40–60 HP) who need a reliable, direct-fit replacement for failing or worn thermostats. Choose this kit when your engine shows warming issues, fluctuating temperatures, or if you’re performing routine cooling-system maintenance and want an OEM-compatible replacement part.