Sierra Thermostat 18-43017, Replaces Indmar S985009, Fits Mercruiser 496 Mag & HO, 8.1L MIE & HO, Pack of 2

The Sierra 18-43017 is a replacement marine engine thermostat sold as a package of 2, giving boat owners a matched pair on hand for a complete cooling system service. It is manufactured to replace Indmar S985009 and is built for the closed cooling systems used on Mercruiser 496 Mag & HO engines and 8.1L MIE & HO engines, where consistent thermostat performance is critical to keeping engine operating temperature within the manufacturer's designed range.

A marine thermostat like the 18-43017 regulates coolant flow by opening and closing in response to engine temperature, preventing overheating during operation and helping the engine reach proper operating temperature more quickly after startup. Replacing a worn or stuck thermostat is a routine part of marine engine cooling system maintenance and is commonly done alongside a gasket change during a full thermostat service. Because the 18-43017 is sold two to a package, it is a convenient option for owners servicing twin-engine boats or keeping a spare on board.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-43017
• Product Type: Thermostat
• Package Quantity: Pack of 2 (priced per package)
• Weight: 0.15 pounds
• UPC: 808282341985

Fitment

• Mercruiser 496 Mag & HO
• Mercruiser 8.1L MIE & HO

Replaces (OEM)

• Indmar S985009

Frequently Asked Questions

What engines does the Sierra 18-43017 thermostat fit? The Sierra 18-43017 thermostat fits Mercruiser 496 Mag & HO engines and Mercruiser 8.1L MIE & HO engines.

What OEM part number does the 18-43017 replace? The Sierra 18-43017 replaces Indmar S985009, so it can be used as a direct equivalent on applicable engines.

How many thermostats come in one package of 18-43017? Two thermostats are included in each package of the Sierra 18-43017, and the item is priced per package of 2.

How much does the Sierra 18-43017 thermostat weigh? Each package of the Sierra 18-43017 weighs 0.15 pounds.

What is the UPC for the Sierra 18-43017? The UPC for the Sierra 18-43017 thermostat is 808282341985.

Is a gasket included with the Sierra 18-43017 thermostat? No, the Sierra 18-43017 package includes the thermostats only; a matching thermostat gasket should be ordered separately when servicing the cooling system.

Why would I replace a marine engine thermostat like the 18-43017? A marine thermostat regulates coolant flow to keep the engine at its proper operating temperature, and a worn or stuck unit like those replaced by the 18-43017 can cause overheating or slow warm-up, making periodic replacement part of routine cooling system maintenance.

Can I use the 18-43017 on a single-engine boat if it comes as a pack of 2? Yes, the Sierra 18-43017 is sold as a package of 2 thermostats, which works well for single-engine boats needing a spare on hand or for twin-engine boats being serviced at the same time.

Is the Sierra 18-43017 an OEM or aftermarket thermostat? The Sierra 18-43017 is an aftermarket replacement thermostat manufactured to replace the OEM Indmar S985009 part on applicable Mercruiser engines.

What category of product is the Sierra 18-43017? The Sierra 18-43017 is a marine engine thermostat used in the cooling system of Mercruiser 496 Mag & HO and 8.1L MIE & HO engines.