Thermostat – Fits Tohatsu/Nissan 3.5HP-40HP (Replaces 350-01030, 346-01030, 3H6-01030-0)
Thermostat – Fits Tohatsu/Nissan 3.5HP-40HP (Replaces 350-01030, 346-01030, 3H6-01030-0) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Thermostat – Fits Tohatsu/Nissan 3.5HP-40HP (Replaces 350-01030, 34...
Product Details
This replacement Thermostat for Tohatsu/Nissan Outboard Motors is designed for a precise fit on a wide range of 2-stroke and 4-stroke engines from 2HP to 50HP. It ensures your engine operates at the correct 50°C (122°F) temperature, providing stable performance for models including the Tohatsu MFS and M series, and Nissan NS series.
It serves as a direct interchange for Tohatsu part numbers 350-01030, 350-01030-1, 346-01030, 346-01030-0, 346-01030-1, 3H6-01030-0, and Nissan 345-01030-0, 345-01030-1.
- Engineered as a direct OEM-spec replacement for straightforward installation.
- Features a durable, corrosion-resistant stainless steel housing and spring-loaded design.
- Includes the required thermostat, gasket, and O-rings for a complete service.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket suppliers.
| Brand | Part Number |
|---|---|
| Tohatsu | 350-01030 / 350-01030-1 |
| Tohatsu | 346-01030 / 346-01030-0 / 346-01030-1 |
| Tohatsu | 3H6-01030-0 |
| Nissan | 345-01030-0 / 345-01030-1 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Tohatsu Engines: This part fits various 4-stroke and 2-stroke models, primarily those requiring a 50°C thermostat. Check your service manual if unsure.
For Nissan Engines: Compatible with several Nissan outboards, including NS models. Verify your part number matches the references.
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Tohatsu | MFS4B | 4 | 4-Stroke | 350-01030 | |
| Tohatsu | MFS5B | 5 | 4-Stroke | 350-01030 | |
| Tohatsu | MFS6B | 6 | 4-Stroke | 350-01030 | |
| Tohatsu | MFS4C | 4 | 4-Stroke | 350-01030 | |
| Tohatsu | MFS5C | 5 | 4-Stroke | 350-01030 | |
| Tohatsu | MFS6C | 6 | 4-Stroke | 350-01030 | |
| Tohatsu | Various models | 3.5-40 | 4-Stroke | 350-01030 | With 50°C thermostat requirement |
| Nissan | NS3.5B2 | 3.5 | 4-Stroke | 346-01030 | |
| Nissan | NS5B2 | 5 | 4-Stroke | 346-01030 | |
| Nissan | NS6B2 | 6 | 4-Stroke | 346-01030 | |
| Nissan | NS40D2 | 40 | 346-01030 | ||
| Nissan | NS30D2 | 30 | 346-01030 | ||
| Nissan | NS25D2 | 25 | 346-01030 |
Technical Specs
- Product Type
- Thermostat
- Installation
- Direct OEM replacement
- Temperature Rating
- 50°C (122°F)
- Housing Material
- Stainless steel
- Operating Temperature
- 50°C (122°F) opening temperature
- Other Technical Attributes
- Spring-loaded design with corrosion-resistant components
What’s in the Box
- 1 x Thermostat (350-01030/346-01030/3H6-01030-0)
- 2 x Rubber O-rings
- 1 x Gasket
Installation Notes
- Ensure the engine is off and cool. Disconnect the battery.
- Drain the engine coolant into a suitable container.
- Locate the thermostat housing on the engine block or cylinder head.
- Remove the bolts securing the housing cover.
- Carefully remove the old thermostat, gasket, and any O-rings. Note the orientation of the thermostat.
- Thoroughly clean the mating surfaces of the housing and cover, removing all old gasket material.
- Install the new thermostat in the correct orientation.
- Place the new gasket and O-rings in position.
- Re-install the housing cover and tighten bolts to the manufacturer’s specified torque.
- Refill the cooling system with the recommended coolant.
- Reconnect the battery, start the engine, and carefully check for any leaks as it warms up.
Troubleshooting & FAQ
What are the signs of a failing thermostat?
Common symptoms include the engine overheating at various speeds, taking too long to reach its normal operating temperature, or erratic temperature gauge readings. A stuck-open thermostat can cause poor fuel economy, while a stuck-closed one will lead to rapid overheating.
How can I confirm this thermostat fits my engine?
The best way is to match your original part number to the ones listed in our Part Number Matrix. You can also check your engine model and horsepower against our compatibility list. If you are unsure, consult your engine’s service manual or contact us with your engine details.
Is this a 50°C or 60°C thermostat?
This is a 50°C (122°F) thermostat. It is crucial to use the correct temperature-rated thermostat for your engine. Using the wrong one can lead to improper engine performance and potential damage.
What is included with the thermostat?
The package contains everything needed for a typical replacement: one thermostat, two rubber O-rings, and one gasket. No other components are included.
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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