Thermostat Cover Gasket – Fits Yamaha 75–225 HP 2-Stroke Outboards (Replaces 688-12414-A1/00)

Thermostat Cover Gasket – Fits Yamaha 75–225 HP 2-Stroke Outboards

This thermostat cover gasket is a direct replacement for a wide range of Yamaha 2-stroke outboard engines from 75 HP to 225 HP, including models from the SX150, S150, and two-stroke HPDI series. It provides a reliable seal for the thermostat housing to the engine block, preventing coolant leaks and ensuring proper engine operating temperature.

This part replaces original Yamaha part numbers 688-12414-00, 688-12414-A0, and 688-12414-A1.

• Installation: Direct replacement for a secure, leak-free fit.
• Function: Seals the thermostat housing against the engine block.
• Compatibility: Engineered for specific Yamaha 2-stroke and 2-stroke HPDI models.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Yamaha owners, here’s a guide to help you identify your engine’s serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

Yamaha 2-Stroke Outboards

Yamaha 2-Stroke HPDI Outboards

Technical Specifications

Package Contents

This package includes:

• 1 x Thermostat Cover Gasket (688-12414-A1)

Explosion Diagram

Installation Guide

1. Safety First: Ensure the engine is completely cool and disconnected from the power source before beginning.
2. Locate Housing: Identify the thermostat housing on the engine block.
3. Remove Cover: Carefully unscrew the bolts holding the thermostat cover in place. Note their placement for reassembly.
4. Remove Old Gasket: Gently lift the cover and remove the old thermostat and gasket. Take care not to drop any components.
5. Clean Surfaces: Meticulously clean both the engine block and thermostat cover mating surfaces. Remove all old gasket material and corrosion.
6. Install New Gasket: Place the new thermostat and gasket into position. Ensure the gasket is properly aligned with the bolt holes.
7. Replace Cover: Re-position the thermostat cover and hand-tighten the bolts.
8. Torque Bolts: Tighten the bolts in a crisscross pattern to the manufacturer's specified torque to ensure an even seal. Do not overtighten.
9. Final Check: Reconnect the power, start the engine, and check for any leaks around the housing as it comes up to temperature.

Troubleshooting & FAQ

Q: How do I confirm this gasket fits my specific engine model?

A: The most reliable method is to match your engine's model and serial number against our compatibility list. You can also compare your existing part number to the cross-reference table provided. For Yamaha owners, our Yamaha Serial Number Guide can help you locate this information.

Q: What are the signs of a failing thermostat gasket?

A: Common signs include visible coolant leaks around the thermostat housing, engine overheating, or fluctuating temperature gauge readings. A visual inspection may reveal a cracked, brittle, or compressed gasket.

Q: How often should I replace the thermostat gasket?

A: It is best practice to replace the thermostat gasket every time the thermostat is serviced or replaced. We recommend checking it as part of your annual engine maintenance schedule.

Q: OEM vs. Aftermarket?

A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?

A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?

A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.