Quicksilver Extended Life Marine Coolant 50/50 Pre-Diluted 1 Gallon — MerCruiser Closed Cooling, Ethylene Glycol

Quicksilver 877770Q1 Extended Life Coolant/Antifreeze is a factory-formulated, pre-diluted 50/50 coolant designed specifically for MerCruiser closed cooling stern drive and inboard gasoline engines.

This one-gallon, pre-mixed formula arrives ready to pour and is engineered to protect marine gasoline engines in closed cooling systems. Quicksilver has produced marine-grade lubricants and fluids for decades, and this coolant is formulated to deliver extended corrosion protection while meeting common ASTM specifications for ethylene glycol-based antifreezes. It’s silicate- and phosphate-free, compatible with conventional antifreeze, and rated to provide extended life performance without gelling.

What engines and cooling systems is this coolant made for?

This product is tailored for MerCruiser closed cooling systems used in stern drive and inboard gasoline engines. Always consult your boat or engine owner’s manual for compatibility and maintenance intervals before use. It’s formulated to perform within the parameters set by Mercury Marine equipment requirements.

• Intended for MerCruiser closed cooling stern drive and inboard gasoline engines
• Pre-diluted 50/50 for immediate use—no mixing required
• Compatible with many conventional ethylene-glycol antifreezes
• Check vehicle manual or service guide for model-specific guidance

How long does the protection last and what standards does it meet?

The formula is engineered to deliver extended life protection for up to five years or 1,000 operating hours under recommended conditions. It meets key industry standards to ensure predictable freeze and boil protection while offering corrosion control for closed-loop marine cooling systems.

• Provides up to 5 years or 1,000 operating hours of protection
• Meets ASTM D-3306 and ASTM D-4340 specifications
• Designed for closed cooling systems where extended service intervals are desired
• Silicate- and phosphate-free to reduce deposit formation

What are the mixture, composition, and handling points I should know?

The product is ethylene glycol-based and comes pre-mixed with de-ionized water at a 50/50 ratio, so it’s ready to use straight from the bottle. Because it’s pre-diluted, you avoid measurement errors and can top off or replace coolant without further mixing. Follow standard safety and disposal practices for coolant fluids.

• Ethylene glycol base, pre-diluted to a 50/50 mix with de-ionized water
• Will not cause gelling when used as directed
• Compatible with many conventional antifreeze products for service flexibility
• Observe local regulations for disposal and avoid ingestion or contact with pets

How does this coolant help with maintenance and engine longevity?

Using a manufacturer-formulated coolant helps maintain corrosion control and thermal stability in closed-loop systems, which supports reliable engine operation over time. Regularly scheduled coolant changes and monitoring reduce the risk of localized corrosion, scale, and heat-transfer loss that can shorten component life.

• Helps protect internal passages and heat exchangers from corrosion
• Maintains freeze and boil-over protection when kept at recommended levels
• Reduces risk of deposits by being silicate- and phosphate-free
• Pre-diluted convenience cuts service time and mixing errors

Who is this for: Boaters, mechanics, and service shops that operate MerCruiser stern drive or inboard gasoline engines and prefer a ready-to-use, manufacturer-compatible coolant. It’s a practical choice for anyone looking to follow factory maintenance guidance, extend service intervals, and simplify coolant replacement with a trusted Quicksilver product.