Sierra 18-3652 Thermostat Kit for Mercruiser 496 Mag & HO, 8.1L MIE & HO, Replaces Mercury 863358T

The Sierra 18-3652 Thermostat Kit is a complete engine cooling system repair kit built for Mercruiser 496 Mag & HO and 8.1L MIE & HO stern drive engines. Replacing a worn or stuck thermostat is one of the most common maintenance tasks on these engines, and this kit supplies everything needed to do the job in one purchase rather than sourcing the thermostat and gaskets separately. The kit is built around a 160 degree Fahrenheit thermostat (Sierra part 18-3552, O.E. #76270), which regulates engine coolant flow to keep the engine within its proper operating temperature range. Running too cool or too hot can reduce engine efficiency and accelerate wear, so a properly functioning thermostat is essential to reliable operation.

Along with the thermostat, the kit includes two thermostat cover gaskets: Sierra part 18-2555 (O.E. #27-89656-1) and Sierra part 18-2843 (O.E. #27-74830), ensuring a proper seal at the thermostat housing and eliminating the need to source gaskets separately or reuse old, hardened ones. Sierra engineers its cooling system components to meet or exceed the original equipment parts they replace, and the 18-3652 kit is manufactured to fit directly in place of the original Mercury thermostat assembly on the specified engines, with no modification required.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3652
• Temperature Rating: 160 degrees Fahrenheit
• Weight: 0.16 pounds
• Color: White
• Unit Count: 1
• Included Components: Thermostat (18-3552), Thermostat Cover Gasket (18-2555), Thermostat Cover Gasket (18-2843)
• OEM Cross Reference: Mercury 863358T, 8M0074922, 8M0076464
• UPC: 030999316165

Fitment

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

Replaces (OEM)

• Mercury 863358T
• Mercury 8M0074922
• Mercury 8M0076464

Frequently Asked Questions

What does the Sierra 18-3652 thermostat kit include? The kit includes a 160 degree Fahrenheit thermostat (Sierra 18-3552) plus two thermostat cover gaskets (Sierra 18-2555 and Sierra 18-2843), giving you everything needed to replace the thermostat and reseal the housing in one purchase.

What engines does the Sierra 18-3652 thermostat kit fit? This kit is designed for Mercruiser 496 Mag & HO and 8.1L MIE & HO stern drive engines.

What temperature rating is the thermostat in kit 18-3652? The thermostat included in the Sierra 18-3652 kit is rated to open at 160 degrees Fahrenheit.

Does the Sierra 18-3652 kit replace Mercury OEM parts? Yes, Sierra 18-3652 cross-references to Mercury part numbers 863358T, 8M0074922, and 8M0076464.

How much does the Sierra 18-3652 thermostat kit weigh? The Sierra 18-3652 thermostat kit weighs 0.16 pounds.

Do I need to buy gaskets separately for a thermostat replacement? No, the Sierra 18-3652 kit already includes both required thermostat cover gaskets (18-2555 and 18-2843), so no separate gasket purchase is needed.

Is the Sierra 18-3652 thermostat kit made to OEM standards? Sierra manufactures its cooling system parts, including the 18-3652 kit, to meet or exceed the specifications of the original equipment parts they replace.

Can I reuse the old thermostat cover gasket instead of the ones in the kit? It is not recommended; the Sierra 18-3652 kit supplies fresh gaskets (18-2555 and 18-2843) specifically because reused gaskets can leak once they have been compressed and heat-cycled.

What is the individual thermostat part number inside kit 18-3652? The thermostat itself is Sierra part 18-3552, corresponding to O.E. Number 76270.

Will the Sierra 18-3652 kit fit any Mercruiser engine? No, fitment is specific to the Mercruiser 496 Mag & HO and 8.1L MIE & HO engines, so buyers should confirm their engine model matches before ordering.

What color is the thermostat in the 18-3652 kit? The thermostat included with Sierra 18-3652 is white.