Thermostat Kit – Fits Volvo Penta/OMC 4.3L/5.0L/5.7L/5.8L V6/V8 (Replaces 3856961, 18-3677)
Thermostat Kit – Fits Volvo Penta/OMC 4.3L/5.0L/5.7L/5.8L V6/V8 (Replaces 3856961, 18-3677) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Thermostat Kit – Fits Volvo Penta/OMC 4.3L/5.0L/5.7L/5.8L V6/V8 (Re...
Product Details
This Thermostat Kit – Fits Volvo Penta/OMC 4.3L/5.0L/5.7L/5.8L V6/V8 (Replaces 3856961, 18-3677) is engineered for a broad range of Volvo Penta and OMC Cobra sterndrive engines from 1993 to 2003. It's designed for both V6 (4.3L) and V8 (5.0L, 5.7L, 5.8L) applications, ensuring proper engine operating temperature.
It serves as a direct replacement for Volvo Penta part numbers 3856961 and 383307, OMC 18-3677 and 47-3677, and Sierra 18-3677, providing a reliable interchange solution.
- Maintains a consistent engine temperature of 160°F (71°C).
- Designed for direct, hassle-free installation.
- Includes the thermostat, gasket, and O-ring needed for a complete service.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Volvo Penta | 3856961 |
| Volvo Penta | 383307 |
| OMC | 18-3677 |
| OMC | 47-3677 |
| Sierra | 18-3677 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit fits the following Volvo Penta models:
| Brand | Model | Stroke | Years | OEM Part No. |
|---|---|---|---|---|
| Volvo Penta | 4.3GL | 4-Stroke | 1993–2002 | 3856961 |
| Volvo Penta | 4.3GS | 4-Stroke | 1993–2002 | 3856961 |
| Volvo Penta | 4.3Gi | 4-Stroke | 1993–2002 | 3856961 |
| Volvo Penta | 5.0FL | 4-Stroke | 1993–1996 | 3856961 |
| Volvo Penta | 5.0Fi | 4-Stroke | 1993–1996 | 3856961 |
| Volvo Penta | 5.0GL | 4-Stroke | 1997–2003 | 3856961 |
| Volvo Penta | 5.0GXi | 4-Stroke | 1997–2003 | 3856961 |
| Volvo Penta | 5.7GL | 4-Stroke | 1993–2003 | 3856961 |
| Volvo Penta | 5.7Gi | 4-Stroke | 1993–2003 | 3856961 |
| Volvo Penta | 5.8FL | 4-Stroke | 1993–1996 | 3856961 |
| Volvo Penta | 5.8Fi | 4-Stroke | 1993–1996 | 3856961 |
| Volvo Penta | 5.8FSi | 4-Stroke | 1993–1996 | 3856961 |
This kit also fits the following OMC Cobra models:
| Brand | Model | Stroke | Years | OEM Part No. |
|---|---|---|---|---|
| OMC | 4.3L | 4-Stroke | 1994–1997 | 18-3677 |
| OMC | 4.3HO | 4-Stroke | 1991–1997 | 18-3677 |
| OMC | 5.0L | 4-Stroke | 1994–1997 | 18-3677 |
| OMC | 5.8L | 4-Stroke | 1993–1997 | 18-3677 |
| OMC | 5.8EFI | 4-Stroke | 1993–1997 | 18-3677 |
Technical Specs
- Product Type
- Marine Engine Thermostat Kit
- Installation
- Direct replacement
- Temperature Rating
- 160°F (71°C)
What’s in the Box
- 1 x Thermostat (Replaces 3856961)
- 1 x Gasket (Replaces 3852111)
- 1 x O-Ring (Replaces 3852071)
Installation Notes
- Disconnect the battery for safety.
- Place a container beneath the engine drain plugs and drain the coolant completely.
- Locate the thermostat housing on the engine, typically where the main coolant hose connects.
- Loosen and remove the bolts securing the housing cover.
- Carefully remove the old thermostat, gasket, and O-ring. Note the thermostat's orientation.
- Thoroughly clean the mating surfaces of the housing and cover, removing any old gasket material or corrosion.
- Install the new thermostat in the correct orientation. Place the new gasket and O-ring into position.
- Re-secure the housing cover and tighten the bolts to the manufacturer's recommended torque. Do not overtighten.
- Refill the cooling system with the appropriate marine-grade coolant.
- Reconnect the battery, start the engine, and let it reach operating temperature while checking for any leaks around the housing. Top off coolant if necessary.
Troubleshooting & FAQ
How do I confirm this kit fits my specific engine?
Your model and year should be listed in the Engine & Model Compatibility tables. Always cross-reference your original part number with those in the Part Number Matrix to ensure an exact match.
What are common signs of a failing thermostat?
Symptoms include engine overheating, the engine not reaching its normal operating temperature (running too cool), or erratic readings on the temperature gauge. These can lead to poor performance, increased fuel consumption, or severe engine damage.
How often should a marine thermostat be replaced?
It is good practice to inspect the thermostat annually and replace it every 2-3 years as part of preventative maintenance, especially if operating in saltwater. Always follow your engine manufacturer's service recommendations.
Why is a 160°F thermostat used?
A 160°F (71°C) rating is standard for many raw water cooled marine engines. It allows the engine to reach a temperature high enough for efficient combustion while preventing overheating and salt/mineral buildup that can occur at higher temperatures.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, it is batch-inspected for consistency and reliability.
Shipping speed & cost?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchase. If anything differs—even if your model appears compatible—do not order.
- This is an aftermarket replacement part, not an original equipment manufacturer (OEM) component.
- Professional installation is highly recommended for safety, performance, and to prevent engine damage.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world conditions.
- Fast Global Fulfillment — We offer free standard delivery to most regions with a typical transit time of 5–15 days.
- Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.
Payment & Security
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