Thermostat – Fits Yamaha 60HP/70HP Outboards (Replaces 6H3-12411-11-00, 18-3622)

Product Details

This aftermarket Thermostat – Fits Yamaha 60HP/70HP Outboards and is designed for direct OEM replacement. It ensures proper engine temperature regulation for Yamaha 2-Stroke 60HP and 70HP outboards manufactured between 1984–2009, including Commercial (C), Endurance (E), and Pro (P) series engines.

This part provides a direct interchange for Yamaha part numbers 6H3-12411-11-00, 6H3-12411-10-00, 6H3-12411-01-00, and 6H3-12411-00-00, as well as Sierra equivalents 18-3622 and 18-3540.

• Installs as a direct OEM-equivalent replacement.
• Maintains a consistent 50°C (122°F) operating temperature.
• Engineered for marine cooling system applications.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This thermostat is compatible with a wide range of Yamaha 60HP and 70HP 2-stroke outboard models produced from 1984 to 2009.

Technical Specs

Product Type

Engine Thermostat

Installation

Direct OEM Replacement

Operating Temperature

50°C (122°F)

Weight

50 Grams (0.11 lbs)

Purpose

For cooling system temperature regulation

What’s in the Box

• 1 x Thermostat (6H3-12411-11-00)

Installation Notes

1. Ensure the engine is off, cool, and disconnected from the battery.
2. Place a drain pan under the engine and drain the cooling system.
3. Locate the thermostat housing on the engine block or cylinder head.
4. Remove the bolts securing the housing cover. Note their positions if they are different lengths.
5. Carefully remove the housing cover. If it is stuck, tap it gently with a rubber mallet; do not pry it open.
6. Remove the old thermostat and any existing gasket or sealant.
7. Thoroughly clean both the housing and cover mating surfaces to remove all old gasket material and corrosion.
8. Install the new thermostat, ensuring it is oriented correctly (the jiggle valve or bleed hole should typically face up). A new gasket is highly recommended.
9. Reinstall the housing cover and tighten the bolts to the manufacturer's specified torque in a crisscross pattern.
10. Refill the cooling system with the appropriate coolant mixture.
11. Reconnect the battery, start the engine, and check for any leaks around the housing as the engine warms up.
12. Monitor the engine temperature to ensure it stabilizes in the normal operating range.

Troubleshooting & FAQ

Safety & Important Info

• Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
• Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.