Mercury – Quicksilver Thermostat Kit | Cooling System Component | 140°F Thermostat & Cork Gasket | 59078Q3

Overview

The right temperature makes all the difference in performance. The Mercury Marine 59078Q3 Quicksilver Thermostat Kit helps older MerCruiser inline 4- and 6-cylinder engines maintain steady, efficient operating temperatures. Designed for GM-built MerCruiser engines, this kit includes a 140°F thermostat and a cork gasket for a complete, ready-to-install replacement. It’s a straightforward, durable solution that keeps your engine running cool, fuel-efficient, and protected from heat-related wear.

Key Features

• Purpose: Regulates coolant flow to maintain optimal 140°F operating temperature.
• Contents: Includes 140°F thermostat and cork gasket for a complete installation.
• Material: Built from marine-grade metal components for corrosion resistance and long life.
• Performance: Helps your engine warm up quickly and stay at the correct temperature under load.
• Ease of Use: Direct-fit design makes replacement simple with standard tools.
• Durability: Withstands the constant heat cycles and vibration of marine use.

Engine & Boat Compatibility

• Older MerCruiser inline 4-cylinder engines (General Motors-based)
• Older MerCruiser inline 6-cylinder engines (General Motors-based)

Performance & Real-World Benefits

The 59078Q3 thermostat kit keeps your cooling system running right by maintaining a consistent temperature balance. The 140°F thermostat ensures your engine warms up fast, runs cleanly, and avoids overheating. The included cork gasket forms a tight, leak-free seal, preventing coolant loss and maintaining pressure throughout the system.

A properly functioning thermostat helps improve efficiency, reduce wear, and protect your motor from heat damage. Replacing it during routine maintenance is an easy step that helps extend the life of your MerCruiser engine.

Why Choose Mercury OEM

The Quicksilver 59078Q3 is a genuine Mercury Marine kit, designed specifically for older MerCruiser engines built by GM. Aftermarket thermostats might look the same but often open at the wrong temperature or use poor sealing materials.

Mercury OEM parts are precision-calibrated and tested for marine performance, ensuring accurate operation and a proper fit. You can count on Mercury’s engineering to deliver reliable temperature control, season after season.

FAQ

Q1: What engines does this thermostat kit fit?
It fits older MerCruiser inline 4- and 6-cylinder engines built by General Motors.

Q2: What temperature does the thermostat open at?
It’s rated for 140°F, the ideal temperature for efficient engine operation.

Q3: What’s included in the kit?
You get the thermostat and a cork gasket for complete replacement.

Q4: Is it hard to install?
Not at all — it’s a direct-fit replacement that can be installed with basic tools.

Q5: Why choose OEM over aftermarket?
Mercury’s OEM parts are factory-calibrated for marine performance and tested to ensure durability and precise fit.