Sierra Thermostat Kit 18-3568, 160 Degree F, MerCruiser Closed Cooling 7.4L 454 V-8, Replaces Mercruiser 99155T1

The Sierra 18-3568 Thermostat Kit is a complete replacement thermostat and seal set built for closed-cooling MerCruiser V-8 engines. It supplies a 160 degree F thermostat along with a matching seal, giving the cooling system the correct opening temperature to keep engine operating temperature in the proper range. Marine thermostats regulate coolant flow between the engine block and the heat exchanger, and using the correct temperature rating and a fresh seal at each replacement helps prevent leaks and overheating.

This kit is designed for MerCruiser 7.4L EFI MIE FWC 454 cid V-8 engines and is also compatible with GM V-6 and V-8 engines equipped with closed cooling. It is built to meet or exceed the performance of the original equipment part it replaces, and it is interchangeable with Mercruiser part number 99155T1, making it a straightforward replacement when the factory thermostat or seal fails or when performing routine cooling system maintenance. The kit ships complete with the thermostat and seal needed to complete the job in a single purchase, without having to source separate components.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3568
• Product Type: Thermostat Kit
• Thermostat Temperature Rating: 160 degrees F
• Cooling System Type: Closed Cooling
• Included Components: Thermostat (18-3555), Thermostat Seal (18-1508)
• Weight: 0.17 pounds
• UPC: 808282112783

Fitment

• MerCruiser 7.4L EFI MIE FWC 454 cid V-8 (1996-1997), closed cooling
• GM V-6 & V-8 engines with closed cooling (1998 & newer)

Replaces (OEM)

• Mercruiser 99155T1

Frequently Asked Questions

What temperature does the Sierra 18-3568 thermostat open at? The Sierra 18-3568 thermostat kit opens at 160 degrees F.

What is included in the Sierra 18-3568 thermostat kit? The kit contains a thermostat (part 18-3555) and a thermostat seal (part 18-1508), everything needed to complete the replacement.

What engines does the Sierra 18-3568 thermostat kit fit? It fits MerCruiser 7.4L EFI MIE FWC 454 cid V-8 engines (1996-1997) with closed cooling, as well as GM V-6 and V-8 engines with closed cooling (1998 and newer).

Does the 18-3568 kit work with raw water or standard cooling systems? No, the Sierra 18-3568 is designed specifically for closed-cooling systems, not standard raw water cooling.

Is the Sierra 18-3568 interchangeable with any Mercruiser part number? Yes, the 18-3568 thermostat kit is interchangeable with Mercruiser 99155T1.

How much does the Sierra 18-3568 thermostat kit weigh? It weighs 0.17 pounds.

Is the Sierra 18-3568 an OEM or aftermarket part? It is an aftermarket replacement kit that Sierra states meets or exceeds the performance of the original equipment part it replaces.

Do I need to replace the thermostat seal along with the thermostat? Yes, and the 18-3568 kit makes this easy since it already includes both the 18-3555 thermostat and the 18-1508 seal in one package.

What is the UPC code for the Sierra 18-3568 thermostat kit? The UPC for the Sierra 18-3568 Thermostat Kit is 808282112783.

How is the 18-3568 different from Sierra's 18-3647 thermostat kit? The 18-3568 is built for closed-cooling MerCruiser 7.4L EFI MIE FWC engines (1996-1997), while the 18-3647 covers the same 7.4L EFI MIE engine and years but for standard cooling instead of closed cooling.

Will the 18-3568 kit fix an overheating MerCruiser engine? A stuck or incorrectly rated thermostat is a common cause of marine engine overheating, and installing the correctly rated 160 degree F Sierra 18-3568 kit with a new seal addresses that specific failure point on closed-cooling MerCruiser 454 V-8 engines.