1. Technical Specifications

2. Key Features

• Precision Thermal Actuation: Incorporates a calibrated wax element engineered for rapid thermal response and strict opening-temperature repeatability, maximizing thermal efficiency and fuel economy.

• Marine Saltwater & Scaling Resistance: Constructed from high-spec marine brass and stainless steel hardware to prevent verdigris oxidation, galvanic corrosion, and mineral scale binding in raw seawater.

• Heavy-Duty Return Spring: Stainless alloy spring maintains consistent seated tension over thousands of heat cycles, preventing cold-engine coolant bypass leaks.

• Direct OEM Bolt-on Fitment: Flange diameter, stroke clearance, and sealing seat dimensions strictly conform to factory drawings for simple drop-in replacement.

3. Compatible Models

Primarily compatible with Mercury and Mariner FourStroke outboard motors:

• Mercury 25 HP / 30 HP Series: 25 HP, 30 HP FourStroke EFI (3-cylinder platforms)

• Mercury 40 HP / 50 HP / 60 HP Series: 40 HP, 50 HP, 60 HP FourStroke EFI and Command Thrust (CT) models

• Mercury SeaPro & Pro XS Series: Commercial and high-performance four-stroke models using this thermostat specification

4. Aftermarket & Brand Compatibility

• OEM Brand Fitment:

• Mercury / Mariner / Quicksilver: Designed for genuine Mercury 25HP through 60HP FourStroke engine thermal regulation systems.

• PREMARINE Brand Aftermarket Replacement:

• PREMARINE Quality Standard: PREMARINE specializes in high-reliability marine cooling, thermal control, and powertrain components. This thermostat assembly is manufactured with precision-calibrated thermal pellets and anti-corrosion metals.

• Direct OEM-Level Performance: Thermal opening curves, stroke lift height, and valve sealing integrity meet or exceed OEM specifications, protecting engines from "making oil" (fuel dilution) and overheating during marine service overhauls.

5. Common Symptoms & Troubleshooting

• Engine Running Too Cold / "Making Oil" (Fuel Diluting Engine Oil):

• Cause: Thermostat stuck in the "open" position due to debris, corrosion, or scale, preventing the engine from reaching operating temperature.

• Troubleshooting: Remove the thermostat and inspect the valve seat; if light passes through the cold valve or it fails to close fully, replace the thermostat immediately.

• Engine Overheating Alarm at Cruising Speed:

• Cause: Thermostat wax pellet has leaked or seized, failing to open and blockading cooling water circulation through the powerhead.

• Troubleshooting: Submerge the thermostat in a water pot with a thermometer and heat to 60°C (140°F); if the valve fails to open fully, replace the unit.

• Coolant Weeping or Salt Crusting Around the Thermostat Cover:

• Cause: Flattened or degraded rubber housing gasket allowing pressurized cooling water to seep past the cover flange.

• Troubleshooting: Always inspect and replace the rubber thermostat seal ring whenever inspecting or renewing the thermostat.

OEM Part Numbers

Compatible OEM references include:

850055001

850055T1

850055A1

850055

Compatible Engine Models

This Thermostat is primarily designed for:

4-Stroke 25/30/40/50/60HP

If you are unsure about compatibility, please provide your engine model number or identification plate for verification before ordering.

Applications

This Thermostat is commonly used for:

Outboard engine repair

Engine rebuilding projects

Marine maintenance workshops

Boat fleet maintenance

Commercial fishing vessels

Recreational boats

Marine spare parts distribution