140°F Thermostat Kit – Fits OMC Cobra/Volvo Penta 7.4L-8.2L V6/V8 (Replaces 3853983, 18-3676)

140°F Thermostat Kit – Fits OMC Cobra/Volvo Penta 7.4L-8.2L V6/V8

This marine thermostat kit is engineered for specific OMC Cobra and Volvo Penta sterndrive engines, ensuring your engine maintains the correct operating temperature. It is designed to maintain a 140°F (60°C) temperature for 7.4L (1994–98) and 8.2L (1998) OMC engines and all 7.4L and 8.2L Volvo Penta models from 1993 forward.

This kit serves as a direct replacement for OMC Stern Drive parts 3853983, 312797, and 307239; Volvo Penta parts 3853983, 3852071, and 835417; Sierra 18-3676; Mallory 9-43026; and QuickMarine 18-3676.

• Maintains Optimal Temperature: Regulates engine temperature at 140°F (60°C) for improved performance and longevity.
• Complete Assembly: Includes the thermostat, O-ring, and gasket for a comprehensive installation.
• Engine-Mounted Design: Designed for direct installation in the engine's thermostat housing.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below.

OMC Cobra

Volvo Penta

Technical Specifications

Package Contents

• 1 x Thermostat (3853983)
• 1 x O-Ring (3852071 / 18-7170)
• 1 x Thermostat Gasket (835417 / 18-0398)

Installation Guide

1. Ensure the engine is completely cool before starting. Disconnect the battery for safety.
2. Drain the engine coolant into a suitable container.
3. Locate the thermostat housing on the engine and remove the bolts securing it.
4. Carefully remove the old thermostat and gasket. Note the orientation of the thermostat.
5. Thoroughly clean the mating surfaces of the thermostat housing and the engine block.
6. Install the new thermostat in the correct orientation, followed by the new gasket and O-ring.
7. Re-secure the thermostat housing and tighten the bolts to the manufacturer's specified torque.
8. Refill the cooling system with the appropriate coolant.
9. Reconnect the battery, start the engine, and check for any leaks around the housing.
10. Allow the engine to reach operating temperature, monitoring the temperature gauge to ensure proper function.

Troubleshooting & FAQ

How do I confirm this fits my engine?
Verify your engine's model and year against the compatibility tables provided on this page. Cross-referencing your existing part number with the numbers listed in our "Part Number Cross-Reference" table is the most reliable method to ensure a correct fit.

What are common signs of a failing thermostat?
Symptoms of a faulty thermostat include engine overheating, the engine not reaching normal operating temperature (running too cool), or erratic temperature gauge readings. A thermostat stuck open will prevent the engine from warming up, while one stuck closed will cause overheating.

How often should I replace my engine's thermostat?
While there is no fixed interval, it is good practice to replace the thermostat as part of preventative maintenance every few hundred hours or during any major cooling system service (e.g., water pump replacement). This helps prevent unexpected failures on the water.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.