160°F Thermostat Kit – Fits Volvo Penta/OMC 4.3L, 5.0L, 5.7L, 5.8L (Replaces 3856961, 383307)
160°F Thermostat Kit – Fits Volvo Penta/OMC 4.3L, 5.0L, 5.7L, 5.8L (Replaces 3856961, 383307) is backordered and will ship as soon as it is back in stock.
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160°F Thermostat Kit – Fits Volvo Penta/OMC 4.3L, 5.0L, 5.7L, 5.8L ...
Product Details
This is a complete 160°F Thermostat Kit – Fits Volvo Penta/OMC 4.3L, 5.0L, 5.7L, 5.8L marine engines, designed to maintain optimal operating temperature. It is compatible with Volvo Penta 4.3L, 5.0L (FiP/FLP/GiP/GLP/GL/GXi/OSi), 5.7L (excluding OSi), and 5.8L models. It also fits OMC sterndrive/cobra engines including 4.3L & 5.0L (1994–1997), 4.3L HO (1991–1997), and 5.8L & 5.8 EFI (1993–1997).
This kit serves as a direct replacement for several part numbers, including Sierra 18-3677, Volvo Penta 3856961, OMC 383307, and Mallory Marine 9-43021.
- Engineered for direct-fit installation.
- Maintains engine temperature at a consistent 160°F (71°C).
- Includes thermostat, O-ring, and gasket for a complete installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Sierra | 18-3677 |
| Sierra | 18-3554 |
| Sierra | 18-3617 |
| Volvo Penta | 3856961 |
| Volvo Penta | 3852216 |
| OMC | 383307 |
| Mallory Marine | 9-43021 |
| Mallory Marine | 9-43028 |
| GLM | 13060 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Volvo Penta applications, this kit covers all models of the 4.3L, 5.7L (except OSi), and 5.8L, as well as specific 5.0L series engines.
For OMC applications, this kit is primarily for specified models manufactured between 1991 and 1997.
| Brand | Model | Years | OEM Part No. |
|---|---|---|---|
| Volvo Penta | 4.3L (All Models) | 3856961 | |
| Volvo Penta | 5.0 FiP, FLP, GiP, GLP | 3856961 | |
| Volvo Penta | 5.0 GL, GXi, OSi | 3856961 | |
| Volvo Penta | 5.7 (All Models Except OSi) | 3856961 | |
| Volvo Penta | 5.8 (All Models) | 3856961 | |
| OMC | 4.3L | 1994–1997 | 383307 |
| OMC | 4.3L HO | 1991–1997 | 383307 |
| OMC | 5.0L | 1994–1997 | 383307 |
| OMC | 5.8L | 1994–1997 | 383307 |
| OMC | 5.8 EFI | 1993–1997 | 383307 |
Technical Specs
- Product Type
- Marine Thermostat Kit
- Temperature Rating
- 160°F (71°C)
- Installation
- Direct replacement
- Fuel Type
- Gasoline
- Dimensions
- 10.0" L x 11.5" W x 7.0" H
- Weight
- 0.12 lbs (0.05 kg)
- Warranty
- Limited Lifetime (Sierra)
- Other Technical Attributes
- Used with: O-Ring 3852071, Gasket 3852111
What’s in the Box
- 1 x Thermostat (160°F/71°C) (Replaces 3856961)
- 1 x O-Ring (Replaces 3852071)
- 1 x Gasket (Replaces 3852111)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery.
- Drain the engine coolant into a suitable container until it is below the thermostat housing level.
- Locate the thermostat housing (typically where the main coolant hose connects to the engine block) and remove the bolts.
- Carefully remove the old thermostat and gasket/O-ring. Note the orientation of the original thermostat.
- Thoroughly clean both the housing and engine block mating surfaces to remove any old gasket material or corrosion.
- Install the new thermostat in the correct orientation, followed by the new gasket or O-ring.
- Re-secure the thermostat housing and tighten the bolts to the manufacturer's specified torque.
- Refill the cooling system with the appropriate coolant, checking for any leaks.
- Reconnect the battery, start the engine, and let it reach operating temperature while monitoring for leaks and proper temperature gauge readings.
Troubleshooting & FAQ
How do I know if my engine's thermostat is failing?
Common signs of a faulty thermostat include engine overheating (stuck closed) or taking too long to reach operating temperature (stuck open). You may also notice erratic temperature gauge readings or poor engine performance.
Is this the correct temperature rating for my engine?
This 160°F thermostat is the standard temperature for the specified Volvo Penta and OMC gasoline engines. Using the correct temperature thermostat is critical for engine performance, fuel efficiency, and longevity.
What is the difference between a thermostat, O-ring, and gasket in this kit?
The thermostat is the valve that regulates coolant flow. The O-ring and gasket are seals used to prevent coolant leaks from the thermostat housing. This kit includes all necessary components for a leak-free installation.
How often should a marine thermostat be replaced?
While there is no fixed interval, it is good practice to inspect the thermostat during routine cooling system service (every 2-3 years) and replace it if there are any signs of corrosion or if engine temperature issues arise.
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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