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SeaSierra

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

$13.00

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Orders are typically processed within 1–2 business days.


U.S. orders usually arrive within 6–15 days, depending on stock location and destination.


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If you have any questions, feel free to email us at info@seasierra.com, and we’ll get back to you within 20–36 hours.

Product Details

This replacement Thermostat Cover Gasket is engineered to fit a wide range of Yamaha 75 HP to 225 HP 2-Stroke outboards, including the SX150, S150, and various HPDI series models. It creates a reliable seal for the thermostat housing, preventing coolant leaks and ensuring proper engine operating temperature.

It serves as a direct replacement for Yamaha part numbers 688-12414-00, 688-12414-A0, and 688-12414-A1, as well as Sierra 18-0844.

  • Ensures a secure seal between the thermostat housing and engine block.
  • Designed for direct, hassle-free installation.
  • Suitable for use in both freshwater and saltwater environments.

Part Number Matrix

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

Brand Part Number
Yamaha 688-12414-00
Yamaha 688-12414-A0
Yamaha 688-12414-A1
Sierra 18-0844

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This gasket fits a wide variety of Yamaha 2-stroke and 2-stroke HPDI outboard engines from 75 to 225 HP.

Brand Model Rated HP Stroke Years OEM Part No. Notes
Yamaha 75A 75 2-Stroke 688-12414-A1
Yamaha E75B 75 2-Stroke 688-12414-A1
Yamaha 75C 75 2-Stroke 688-12414-A1
Yamaha 80A 80 2-Stroke 688-12414-A1
Yamaha 85A 85 2-Stroke 688-12414-A1
Yamaha 90E 90 2-Stroke 688-12414-A1
Yamaha 90A 90 2-Stroke 688-12414-A1
Yamaha 100A 100 2-Stroke 688-12414-A1
Yamaha 115E 115 2-Stroke 688-12414-A1
Yamaha 115A 115 2-Stroke 688-12414-A1
Yamaha E115A 115 2-Stroke 688-12414-A1
Yamaha 115B 115 2-Stroke 688-12414-A1
Yamaha 115C 115 2-Stroke 688-12414-A1
Yamaha 130B 130 2-Stroke 688-12414-A1
Yamaha 140A 140 2-Stroke 688-12414-A1
Yamaha 140B 140 2-Stroke 688-12414-A1
Yamaha 140C 140 2-Stroke 688-12414-A1
Yamaha 150E 150 2-Stroke 688-12414-A1
Yamaha 150A 150 2-Stroke 688-12414-A1
Yamaha 150C 150 2-Stroke 688-12414-A1
Yamaha 150F 150 2-Stroke 688-12414-A1
Yamaha 150G 150 2-Stroke 688-12414-A1
Yamaha D150H 150 2-Stroke 688-12414-A1
Yamaha 150J 150 2-Stroke 688-12414-A1
Yamaha 150L 150 2-Stroke 688-12414-A1
Yamaha D150N 150 2-Stroke 688-12414-A1
Yamaha SX150 150 2-Stroke 688-12414-A1 Saltwater Series
Yamaha S150 150 2-Stroke 688-12414-A1 Saltwater Series
Yamaha 175A 175 2-Stroke 688-12414-A1
Yamaha 175B 175 2-Stroke 688-12414-A1
Yamaha 175D 175 2-Stroke 688-12414-A1
Yamaha 175F 175 2-Stroke 688-12414-A1
Yamaha 200E 200 2-Stroke 688-12414-A1
Yamaha 200A 200 2-Stroke 688-12414-A1
Yamaha 200B 200 2-Stroke 688-12414-A1
Yamaha 200C 200 2-Stroke 688-12414-A1 Pro V 200
Yamaha 200F 200 2-Stroke 688-12414-A1
Yamaha 200G 200 2-Stroke 688-12414-A1
Yamaha 200J 200 2-Stroke 688-12414-A1
Yamaha 220A 220 2-Stroke 688-12414-A1
Yamaha 225A 225 2-Stroke 688-12414-A1
Yamaha 225B 225 2-Stroke 688-12414-A1
Yamaha 225D 225 2-Stroke 688-12414-A1
Brand Model Rated HP Stroke Years OEM Part No. Notes
Yamaha Z150P 150 2-Stroke HPDI 688-12414-A1
Yamaha Z150Q 150 2-Stroke HPDI 688-12414-A1
Yamaha Z175G 175 2-Stroke HPDI 688-12414-A1
Yamaha Z175H 175 2-Stroke HPDI 688-12414-A1
Yamaha Z200N 200 2-Stroke HPDI 688-12414-A1
Yamaha Z200P 200 2-Stroke HPDI 688-12414-A1

Technical Specs

Product Type
Thermostat Cover Gasket
Installation
Direct replacement
Other Technical Attributes
Seals thermostat housing to engine block

What’s in the Box

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

Installation Notes

  1. Ensure the engine is completely cool and disconnect the battery.
  2. Drain the engine coolant to a level below the thermostat housing.
  3. Carefully remove the bolts securing the thermostat cover.
  4. Remove the old cover and gasket. Clean both mating surfaces thoroughly, removing any old gasket material or corrosion.
  5. Place the new gasket onto the engine block or into the recess in the cover.
  6. Reinstall the thermostat cover and tighten the bolts to the manufacturer's specified torque in a crisscross pattern.
  7. Refill the cooling system with the appropriate coolant.
  8. Reconnect the battery, start the engine, and carefully check for any leaks around the housing as it comes up to temperature.

Troubleshooting & FAQ

How do I know if this gasket will fit my engine?

First, check your engine model against the comprehensive compatibility tables on this page. This gasket is designed for a wide range of Yamaha 75-225 HP 2-stroke outboards. The most reliable method is to confirm that the OEM part number 688-12414-A1 is listed for your specific model and year in your engine's service manual.

What are the signs of a failing thermostat cover gasket?

Common symptoms include visible coolant leaks (often leaving a white or colored residue) around the thermostat housing, engine overheating alarms, or white steam from the engine cowling. A failed gasket can lead to improper engine cooling and potential damage.

When should this gasket be replaced?

It is best practice to replace the thermostat gasket whenever you service or replace the thermostat itself. You should also replace it immediately if you notice any signs of leakage or damage during a routine inspection.

What’s the difference between OEM and this aftermarket part?

This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials for a precise fit and reliable seal. All parts are manufactured in an ISO 9002 certified facility and are batch-inspected for quality and consistency.

How fast is shipping?

We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free for most orders. Expedited options, if available for your location, will appear at checkout.

What is the warranty and return policy?

This part is covered by a 1-year warranty against manufacturing defects under normal marine use. If you encounter an issue, please contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. See our full policy page or reach out for instructions.

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.

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