Mercury – Quicksilver Thermostat | Cooling System Component | 140°F Temperature Rating | 59078

Overview

Keeping your engine running at the right temperature is key to performance and longevity. The Mercury Marine 59078 Quicksilver Thermostat is a direct replacement for select MerCruiser sterndrives, maintaining an optimal 140°F operating temperature for efficient cooling and smooth performance. It’s built for MerCruiser 120HP 2.5L, 140HP 3.0L, and 160HP engines, using corrosion-resistant materials that hold up to marine heat, pressure, and salt exposure. Easy to install and precision-calibrated, this thermostat helps your engine stay cool, responsive, and protected season after season.

Key Features

• Purpose: Regulates engine temperature to improve fuel efficiency and prevent overheating.
• Temperature Rating: Opens at 140°F, maintaining the ideal range for MerCruiser cooling systems.
• Material: Made from marine-grade metals designed to resist corrosion and scaling.
• Performance: Ensures quick warm-up and consistent cooling under load.
• Ease of Use: Direct-fit replacement that installs easily using standard tools.
• Durability: Built to withstand marine vibration, heat, and water exposure without sticking or warping.

Engine & Boat Compatibility

• MerCruiser 120HP 2.5L (serial No. 2324347 and above)
• MerCruiser 140HP 3.0L (serial No. 0L340999 and below)
• MerCruiser 160HP

Performance & Real-World Benefits

The 59078 thermostat keeps your engine operating at the perfect balance of temperature and efficiency. Too cold and you’ll waste fuel — too hot and you risk engine damage. This thermostat opens precisely at 140°F, providing a steady flow of coolant to maintain proper heat balance throughout the system.

Its corrosion-resistant design makes it reliable even after years in salt or brackish water. A fresh thermostat helps your engine start easier, run smoother, and maintain consistent power — simple maintenance that pays off every trip.

Why Choose Mercury OEM

The Quicksilver 59078 is a genuine Mercury Marine part, engineered specifically for your MerCruiser engine’s cooling system. Aftermarket thermostats can vary slightly in calibration or material quality, which can affect how your engine warms up or handles temperature changes.

Mercury’s OEM parts are built to precise temperature tolerances and tested for long-term durability in marine conditions. Installing an OEM thermostat ensures your cooling system performs exactly as designed — steady, efficient, and dependable.

FAQ

Q1: What engines does this thermostat fit?
It fits MerCruiser 120HP 2.5L (2324347+), 140HP 3.0L (0L340999 and below), and 160HP engines.

Q2: What temperature does it regulate at?
It opens at 140°F, maintaining consistent cooling performance.

Q3: How hard is it to install?
Installation is simple — remove the old thermostat, clean the housing, and replace with this OEM part.

Q4: Is it made for saltwater use?
Yes — it’s constructed from corrosion-resistant, marine-grade materials.

Q5: Why OEM instead of aftermarket?
Mercury OEM thermostats are factory-calibrated and built to last, guaranteeing proper temperature control and fit.