Outboard Thermostat – Fits Yamaha 2-Stroke & 4-Stroke 2.5-250 HP (Replaces 6E5-12411-30, 688-12411)
Outboard Thermostat – Fits Yamaha 2-Stroke & 4-Stroke 2.5-250 HP (Replaces 6E5-12411-30, 688-12411) is backordered and will ship as soon as it is back in stock.
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Outboard Thermostat – Fits Yamaha 2-Stroke & 4-Stroke 2.5-250 H...
Outboard Thermostat – Fits Yamaha 2-Stroke & 4-Stroke 2.5-250 HP (Replaces 6E5-12411-30, 688-12411) is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket Outboard Thermostat – Fits Yamaha 2-Stroke & 4-Stroke 2.5-250 HP is designed for a broad range of Yamaha engines. It regulates engine temperature for optimal performance, fitting various 2-stroke models from 3 HP to 250 HP and 4-stroke F-series models from 2.5 HP to 100 HP. The thermostat operates at a standard 50°C (122°F) for most 2-stroke applications.
It serves as a direct replacement for multiple OEM and aftermarket part numbers, including Yamaha 6E5-12411-30 and 688-12411 series, Sierra 18-3540, and others, ensuring a precise fit and function.
- Installs as a direct OEM-equivalent replacement.
- Engineered for marine gasoline outboard applications.
- Kit includes the thermostat, gasket, and seal for a complete installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Sierra | 18-3540 |
| Sierra | 18-3622 |
| GHmarine | 18-3540 |
| QuickMarine | 18-3622 |
| Yamaha | 688-12411-00 |
| Yamaha | 688-12411-01 |
| Yamaha | 688-12411-10 |
| Yamaha | 688-12411-11 |
| Yamaha | 6E5-12411-10 |
| Yamaha | 6E5-12411-20 |
| Yamaha | 6E5-12411-30 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This thermostat fits a wide array of Yamaha 2-stroke and 4-stroke outboard engines. Please verify your specific model is listed.
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Yamaha | 75C | 75 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 90A | 90 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 100A | 100 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 115C | 115 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 130B | 130 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 150F, Z150P, Z150Q | 150 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 175D, Z175G | 175 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 200F, 200G, Z200N, Z200P | 200 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 225D | 225 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | 250B | 250 | 2-Stroke | 688-12411, 6E5-12411-30 | |
| Yamaha | Various models | 3-70 | 2-Stroke | 6E5-12411, 688-12411 | Per GHmarine 18-3540 |
| Yamaha | F2.5M | 2.5 | 4-Stroke | Mentioned in eBay listing | |
| Yamaha | Various models | 2.5-100 | 4-Stroke | Per compatibility data |
Technical Specs
- Product Type
- Marine Outboard Engine Thermostat
- Installation
- Direct OEM Replacement
- Fuel Type
- Gasoline
- Housing Material
- Metal
- Operating Temperature
- 50°C (122°F)
- Other Technical Attributes
- Temperature Rating: 50°C (122°F) for 2-stroke applications
What’s in the Box
- 1 x Thermostat (Replaces 688-12411, 6E5-12411-30)
- 1 x Thermostat Housing Gasket (Replaces 688-12414)
- 1 x Thermostat Seal (Replaces 688-12412)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery for safety.
- Locate the thermostat housing on the engine block or cylinder head. Drain a small amount of coolant if necessary.
- Remove the bolts securing the housing cover. Note their placement if they are different lengths.
- Carefully remove the old thermostat and gasket. Clean both mating surfaces of any old gasket material or corrosion.
- Install the new thermostat, ensuring it is correctly oriented. Place the new gasket and seal in position.
- Reinstall the housing cover and tighten the bolts to the manufacturer's specified torque in a crisscross pattern.
- Reconnect the battery, refill any lost coolant, and check for leaks after starting the engine.
Troubleshooting & FAQ
How do I know if this thermostat fits my Yamaha engine?
This thermostat fits a wide range of Yamaha 2-stroke (3-250 HP) and 4-stroke (2.5-100 HP) models. The best way to confirm is by matching your old part number to those listed in our Part Number Matrix, such as 6E5-12411-30 or 688-12411-10. Also, check the compatibility table for your specific engine model.
What is the operating temperature of this thermostat?
The standard temperature rating is 50°C (122°F), which is common for many Yamaha 2-stroke applications. Temperature ratings for 4-stroke engines can vary, so always confirm requirements for your specific model.
What are the signs of a failing outboard thermostat?
Common signs include engine overheating (stuck closed) or slow warm-up (stuck open). You might also notice poor engine performance, increased fuel consumption, or steam from the exhaust at idle. An alarm from your engine's warning system is a clear indicator.
Does this kit include the gasket and seal?
Yes, this kit includes one thermostat, one thermostat housing gasket, and one thermostat seal for a complete replacement.
What's the difference between the 6E5-12411 and 688-12411 part numbers?
These part numbers often refer to thermostats with the same temperature rating and dimensions but may have been used on different engine series or represent supersessions over time. This aftermarket part is designed to be a direct cross-reference for all listed numbers.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our 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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