Thermostat 62°/143°F – Fits Johnson/Evinrude 9.9–300HP Two-Stroke Outboards (Replaces 0778199, 0394411)
Thermostat 62°/143°F – Fits Johnson/Evinrude 9.9–300HP Two-Stroke Outboards (Replaces 0778199, 0394411) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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Thermostat 62°/143°F – Fits Johnson/Evinrude 9.9–300HP Two-Stroke O...
Thermostat 62°/143°F – Fits Johnson/Evinrude 9.9–300HP Two-Stroke Outboards (Replaces 0778199, 0394411) is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket Thermostat 62°/143°F – Fits Johnson/Evinrude 9.9–300HP Two-Stroke Outboards (Replaces 0778199, 0394411) is engineered for consistent engine temperature regulation in a wide range of Johnson/Evinrude 9.9–300HP, 2-Stroke outboards from 1985–1995. It is compatible with various models, including two-cylinder through eight-cylinder engines.
It serves as a direct interchange for OMC/Johnson/Evinrude part numbers 394411, 0394411, 778199, and 0778199, as well as aftermarket equivalents Sierra 18-1506 and GLM 13190.
- Designed as a direct OEM replacement for a hassle-free installation.
- Opens at a precise 62°C (143°F) to ensure optimal engine operating temperature.
- Manufactured with a corrosion-resistant metal housing for durability in marine environments.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket brands.
| Brand | Part Number |
|---|---|
| OMC/Johnson/Evinrude | 394411 / 0394411 |
| OMC/Johnson/Evinrude | 778199 / 0778199 |
| Sierra | 18-1506 |
| GLM | 13190 |
Engine & Model Compatibility
Confirm your engine model and year in the table below to ensure accurate fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Johnson/Evinrude | OMC | 9.9 | 2-Stroke | 1993–1995 | 0778199/0394411 | Big Bore Two-Cylinder |
| Johnson/Evinrude | OMC | 15 | 2-Stroke | 1993–1995 | 0778199/0394411 | Big Bore Two-Cylinder |
| Johnson/Evinrude | OMC | 60 | 2-Stroke | 1989–1990 | 0778199/0394411 | Three-Cylinder |
| Johnson/Evinrude | OMC | 65 | 2-Stroke | 1987–1990 | 0778199/0394411 | Three-Cylinder |
| Johnson/Evinrude | OMC | 70 | 2-Stroke | 1986–1990 | 0778199/0394411 | Three-Cylinder |
| Johnson/Evinrude | OMC | 120 | 2-Stroke | 1985–1990 | 0778199/0394411 | Four-Cylinder |
| Johnson/Evinrude | OMC | 125 | 2-Stroke | 1989–1990 | 0778199/0394411 | Four-Cylinder |
| Johnson/Evinrude | OMC | 140 | 2-Stroke | 1985–1990 | 0778199/0394411 | Four-Cylinder |
| Johnson/Evinrude | OMC | 185 | 2-Stroke | 1989–1990 | 0778199/0394411 | Six-Cylinder |
| Johnson/Evinrude | OMC | 200 | 2-Stroke | 1986–1990 | 0778199/0394411 | Six-Cylinder |
| Johnson/Evinrude | OMC | 225 | 2-Stroke | 1986–1990 | 0778199/0394411 | Six-Cylinder |
| Johnson/Evinrude | OMC | 275 | 2-Stroke | 1985–1988 | 0778199/0394411 | Two-Cylinder/Eight-Cylinder |
| Johnson/Evinrude | OMC | 300 | 2-Stroke | 1985–1990 | 0778199/0394411 | Eight-Cylinder |
Technical Specs
- Product Type
- Outboard Engine Thermostat
- Installation
- Direct OEM Replacement
- Temperature Rating
- 62°C/143°F
- Housing Material
- Corrosion-Resistant Metal
- Operating Temperature
- Opens at 62°C (143°F)
- Other Technical Attributes
- Manufactured to OEM specifications
What’s in the Box
- 1 x Thermostat (Replaces 0778199/0394411)
Installation Notes
- Ensure the engine is off and cool. Disconnect the battery for safety.
- Drain the engine block of coolant to a level below the thermostat housing.
- Locate and carefully remove the thermostat housing cover. Note the orientation of the existing thermostat.
- Remove the old thermostat and gasket. Clean both the housing and cover surfaces thoroughly, removing any old gasket material or sealant.
- Place the new thermostat into the housing in the correct orientation.
- Install a new gasket (sold separately) before reinstalling the housing cover.
- Tighten the housing bolts to the manufacturer's recommended torque specification.
- Refill the cooling system with the appropriate coolant.
- Reconnect the battery, start the engine, and check for any leaks around the housing as the engine warms up.
Troubleshooting & FAQ
How do I know if my thermostat is failing?
Common signs include the engine overheating, running too cool (resulting in poor performance and fuel economy), or erratic temperature gauge readings. If the engine doesn't reach its optimal operating temperature, the thermostat may be stuck open. If it overheats, it may be stuck closed.
What is the correct operating temperature for this thermostat?
This thermostat is designed to start opening at 62°C (143°F), which is the standard manufacturer-specified temperature for the compatible Johnson/Evinrude engine models to ensure efficient operation and prevent overheating.
Can I install this myself?
Yes, this is a common DIY task for individuals with mechanical experience and the right tools. However, to ensure safety and proper cooling system performance, professional installation is always recommended.
Does this thermostat come with a gasket?
This listing includes the thermostat only. It is highly recommended to use a new gasket during installation to ensure a proper seal; gaskets are sold separately.
How often should I replace my outboard's thermostat?
For preventative maintenance, it is good practice to inspect the thermostat annually and consider replacing it every 2-3 years or during any major cooling system service, even if no failure signs are present.
Is this compatible with four-stroke engines?
No, this thermostat is specifically engineered for the 2-stroke Johnson/Evinrude models listed in the compatibility table. Using it in a four-stroke engine can lead to improper cooling and potential engine damage.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It has been built to OEM-level specifications with comparable materials. Our parts are manufactured in an ISO 9002 certified facility and are batch-inspected for quality and consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit is 5–15 days for most regions. Standard shipping is free for most orders, with expedited options available at checkout where applicable.
Warranty & returns
This product 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
- Always verify images and specifications against your original part before purchasing. If anything differs—even if your model appears on the compatibility list—do not purchase.
- This is a high-quality aftermarket replacement component, not an Original Equipment Manufacturer (OEM) part.
- Professional installation is highly recommended for safety, performance, and to prevent damage to your engine.
About Sea Sierra
- Pro-Grade Standards — We supply professional-grade marine parts engineered to meet or exceed OEM-level tolerances and are rigorously tested for real-world conditions.
- Fast Global Fulfillment — With our direct-to-you model, we offer free standard delivery to most regions with a typical transit time of just 5–15 days.
- Manufacturer-Direct Value — By eliminating middlemen, we deliver exceptional value with fair pricing and a commitment to quality control and durable materials.
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