18-3681 1544683 Thermostat 180°F / 82°C for Volvo Penta D4 D6 D12 | JLM Marine

18-3681 1544683 Thermostat 180°F / 82°C for Volvo Penta D4 D6 D12

This 180°F / 82°C thermostat is engineered to fit Volvo Penta D4, D6, and D12 sterndrive engines, covering a wide range of horsepower ratings from 150 HP to 585 HP across model years 1988 and up. Designed to maintain optimal engine operating temperature, this thermostat ensures reliable thermal management for your marine diesel engine.

This aftermarket replacement directly crosses to OEM part numbers 1544683, 1676306, 11000237, 8149182, 1661277, 1303061, and replaces Sierra 18-3681, providing a cost-effective solution without compromising performance.

• Temperature rating: 180°F / 82°C
• Direct fit for Volvo Penta D-series sterndrives
• Complete kit includes thermostat ready for installation

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.

Technical Specifications

Package Contents

This kit contains the following components:

• 1 × Thermostat (180°F / 82°C)

Installation Guide

1. Preparation: Allow the engine to cool completely and disconnect the battery to ensure safety during installation.
2. Drain Coolant: Open the drain plug or remove the lower hose to drain coolant from the system into a suitable container.
3. Access Thermostat Housing: Locate the thermostat housing on your Volvo Penta engine (typically on the front or side of the block). Remove retaining bolts or clamps securing the housing cover.
4. Remove Old Thermostat: Carefully extract the old thermostat and inspect the housing for debris or corrosion.
5. Clean Mating Surfaces: Use a gasket scraper or cloth to remove old gasket material and ensure a clean seal surface on both the housing and cover.
6. Install New Thermostat: Position the new thermostat in the housing with the temperature-sensing element (spring side) facing into the engine block as indicated by directional markings.
7. Apply New Gasket/Sealant: Install a new gasket or apply marine-grade sealant as specified by your engine manual.
8. Reassemble Housing: Reattach the thermostat housing cover and torque bolts to manufacturer specifications in a crisscross pattern.
9. Refill Coolant: Close drain plugs and refill the cooling system with the recommended coolant mixture. Check the coolant reservoir level.
10. Bleed Air: Start the engine and allow it to reach operating temperature while monitoring for leaks. Open the bleed valve if equipped to release trapped air.
11. Check Operation: Verify that the engine reaches normal operating temperature (around 180°F) and that coolant circulates properly through the system.
12. Final Inspection: Recheck all connections, top off coolant as needed, and confirm no leaks are present around the thermostat housing.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my Volvo Penta engine?
A: Cross-reference your engine model (D4, D6, or D12) and year with the compatibility table above. Also verify your original thermostat's OEM part number against the listed cross-references (1544683, 1676306, 11000237, etc.).

Q: What are the signs that my thermostat needs replacement?
A: Common symptoms include engine overheating, slow warm-up times, fluctuating temperature gauge readings, or coolant leaks around the thermostat housing. If the thermostat fails to open, the engine will overheat; if it fails to close, the engine will run too cool.

Q: How often should I replace the thermostat?
A: Thermostats typically last 3–5 years or as recommended in your Volvo Penta maintenance schedule. Replace the thermostat if you experience cooling system issues or during major cooling system service (such as replacing hoses or the heat exchanger).

Q: Can I reuse the old gasket when installing this thermostat?
A: No, always use a new gasket or fresh sealant to ensure a proper seal and prevent coolant leaks. Reusing old gaskets can lead to leaks and compromise cooling system performance.

Q: What is the difference between OEM and aftermarket thermostats?
A: 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.

Q: How fast do you ship and how much does it cost?
A: 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.

Q: What is your warranty and return policy?
A: 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.