Quicksilver 59078Q3 Replacement 140°F Thermostat Kit for MerCruiser Inline 4 & 6-Cylinder Engines

The Quicksilver 59078Q3 is an OEM replacement thermostat kit designed for older MerCruiser inline 4-cylinder and 6-cylinder engines manufactured by General Motors. Operating at a 140°F opening temperature, this kit helps maintain proper engine cooling system performance and prevents overheating on compatible stern drive applications.

This is a genuine Quicksilver part — the Mercury Marine original equipment brand — manufactured to the same stringent OEM specifications as the components originally installed at the factory. Quicksilver replacement parts are engineered specifically for Mercury Marine and MerCruiser engines, ensuring a precise fit and reliable long-term performance.

Kit Includes:

• 140°F replacement thermostat
• Cork thermostat gasket

Key Features:

• OEM Quicksilver part — direct factory replacement
• 140°F thermostat opens at the correct operating temperature for compatible GM inline engines
• Includes cork gasket for a proper, leak-free seal
• Installs with common hand tools
• Refer to your engine owner's manual for thermostat removal and installation procedures

Cross-Reference Part Numbers: 59078Q3, 59078T3, 59078T4, Sierra 18-3650, Sierra 18-3550