Thermostat Kit (160°F/71°C) – Fits OMC Cobra & Volvo Penta 3.8-7.5L V6/V8 (Replaces 383307, 18-3653)

$22.50

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Thermostat Kit (160°F/71°C) – Fits OMC Cobra & Volvo Penta 3.8-7.5L V6/V8 (Replaces 383307, 18-3653) is backordered and will ship as soon as it is back in stock.

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Delivery and Shipping

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If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This Thermostat Kit (160°F/71°C) – Fits OMC Cobra & Volvo Penta 3.8-7.5L V6/V8 is designed for OMC Cobra and Volvo Penta sterndrive engines with V6 and V8 configurations ranging from 3.8L to 7.5L (90-454HP) manufactured from 1968 and up.

It serves as a direct interchange for multiple OEM and aftermarket parts, including Sierra 18-3653, OMC 383307/379754, Volvo Penta 3856961, GLM 13430/13060, and Mallory 9-43156/9-43021.

Direct OEM replacement for straightforward installation.
Maintains engine temperature at a consistent 160°F (71°C).
Includes thermostat and all necessary gaskets for a complete service.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Sierra	18-3653
OMC	383307
OMC	379754
Volvo Penta	3856961
GLM	13430
GLM	13060
Mallory	9-43156
Mallory	9-43021

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For OMC Cobra models, this kit fits various engines by displacement (e.g., 3.8L, 5.7L) and by rated horsepower (e.g., 120, 230) from 1969 onwards.

For Volvo Penta models, this kit fits several popular GL, GS, Gi, FL, Fi, and FSi series engines.

Brand	Model	Rated HP	Years	OEM Part No.
OMC Cobra	3.8L		1981–1985	383307
OMC Cobra	4.3L		1985–1986	383307
OMC Cobra	5.0L		1982–1988	383307
OMC Cobra	5.7L		1982–1988	383307
OMC Cobra	7.5L			383307
OMC Cobra	90	90	1970	383307
OMC Cobra	100	100	1972–1973	383307
OMC Cobra	120	120	1969–1980	383307
OMC Cobra	140	140	1973–1980	383307
OMC Cobra	155	155	1969–1972	383307
OMC Cobra	165	165	1972–1976	383307
OMC Cobra	170	170	1974	383307
OMC Cobra	175	175	1975–1977	383307
OMC Cobra	185	185	1978–1980	383307
OMC Cobra	190	190	1974–1977	383307
OMC Cobra	200	200	1979–1981	383307
OMC Cobra	210	210	1969–1972	383307
OMC Cobra	215	215	1971	383307
OMC Cobra	225	225	1971	383307
OMC Cobra	230	230	1979–1981	383307
OMC Cobra	235	235	1971, 1975–1977	383307
OMC Cobra	240	240	1978	383307
OMC Cobra	245	245	1972–1975	383307
OMC Cobra	250	250	1970–1973, 1979	383307
OMC Cobra	260	260	1979–1981	383307
OMC Cobra	305	305	1977–1982	383307
OMC Cobra	350	350	1977–1982	383307
OMC Cobra	454	454	1977–1982	383307
Volvo Penta	4.3GL			3856961
Volvo Penta	5.7GL			3856961
Volvo Penta	4.3GS			3856961
Volvo Penta	5.7Gi			3856961
Volvo Penta	4.3Gi			3856961
Volvo Penta	5.8FL			3856961
Volvo Penta	5.0FL			3856961
Volvo Penta	5.8Fi			3856961
Volvo Penta	5.0Fi			3856961
Volvo Penta	5.8FSi			3856961

Technical Specs

Product Type: Marine Engine Thermostat Kit
Installation: Direct OEM Replacement
Temperature Rating: 160°F (71°C)
Application: Sterndrive Engines
Fit Type: V6 & V8 Marine Engines
Engine Displacement: 3.8L, 4.3L, 5.0L, 5.7L, 5.8L, 7.5L

What’s in the Box

1 x Thermostat (383307/3856961)
1 x O-ring (3852071)
1 x Gasket (314809)
1 x Gasket (313416)
1 x Housing Gasket (3852111)
1 x Installation Instructions

Installation Notes

Disconnect the negative battery terminal before beginning work.
Drain the engine coolant to a level below the thermostat housing.
Locate and carefully remove the thermostat housing, taking note of hose connections.
Remove the old thermostat and any existing gasket or O-ring material.
Thoroughly clean both the housing and engine mounting surfaces to ensure a proper seal.
Install the new thermostat in the correct orientation, followed by the new gasket(s) and/or O-ring included in the kit.
Re-install the housing and tighten the mounting bolts to the manufacturer's recommended torque specifications.
Reconnect all hoses securely.
Refill the cooling system with the appropriate coolant mixture.
Reconnect the battery, start the engine, and carefully check for any leaks as it warms up.
Monitor the temperature gauge to ensure the engine reaches and maintains its normal operating temperature.

Troubleshooting & FAQ

What are the signs of a failing thermostat?

A faulty thermostat can cause engine overheating if it's stuck closed, or it may lead to prolonged warm-up times, poor fuel economy, and carbon buildup if it's stuck open. Watch your temperature gauge for readings that are higher or lower than normal.

Is this 160°F thermostat correct for my engine?

This 160°F (71°C) rating is the standard specification for the wide range of OMC and Volvo Penta engines listed. It is suitable for both raw-water and fresh-water cooled systems. However, always consult your owner's manual to confirm the specified temperature for your exact model and local operating conditions.

How often should a marine thermostat be replaced?

It is best practice to inspect the thermostat during routine cooling system service (every 2-3 years or 200-300 hours). For engines operated in saltwater, annual inspection and replacement is recommended to prevent failure from corrosion and salt buildup.

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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