Thermostats & Cooling System Parts

An outboard’s cooling system faces a constant battle against varying water temperatures, salt crystallization, and silt accumulation. These genuine Yamaha OEM thermostats are designed to maintain the exact thermal equilibrium your four-stroke or two-stroke powerhead requires. Operating too cold causes raw fuel to bypass the piston rings and dilute the crankcase oil (“making oil”), while running too hot risks severe cylinder distortion, head gasket failure, and catastrophic piston seizing.

Built using high-grade marine brass, copper, and specialized thermal wax pellets, these factory replacements respond instantly to minor temperature shifts, opening cleanly to allow continuous raw water transit. Because changing a thermostat requires breaking the salt-crusted seal of the cylinder head cover, these individual components and comprehensive service kits provide new composition gaskets and anti-corrosive pressure relief valve components (poppet valves). Routinely swapping your thermostat clears out accumulated debris, resets proper engine warming sequences, and ensures optimal combustion efficiency across both icy early-morning launches and high-RPM summer runs.

Variants Available / Compatibility Groups:

• Portable & Mid-Range Series: Compact single-thermostat configurations engineered for inline-2 to inline-4 cylinder blocks (e.g., F25, F40, F60, F90, F115).

• V6 Offshore & V MAX SHO Series (4.2L & 3.3L): High-volume, dual-thermostat kits designed to regulate the massive cooling jackets of high-performance offshore platforms.

• Flagship XTO Offshore Series: Heavy-duty, specialized thermal assemblies tailored for the extreme heat dissipation demands of the 4.3L, 425HP, and 450HP multi-engine configurations.

Key Features:

• Precision-calibrated opening temperatures (typically 50°C to 60°C / 122°F to 140°F depending on engine spec)

• Marine-grade brass and copper construction to eliminate premature structural scaling

• High-elasticity compression gaskets engineered to handle continuous thermal cycling

• Calibrated internal bypass springs to stabilize system pressure before the main valve strokes open

Ideal For: Preventative 100-hour or annual marine checkups, troubleshooting “cold-running” or oil-dilution issues, fixing overheat alarms, and restoring seasonal cooling performance.