Mercury – Extended Life Coolant / Anti-Freeze | Closed Cooling System Care | Pre-Diluted 50/50 | 877770K1

Overview

Every seasoned boater knows the quiet kind of confidence that comes from lifting the engine hatch and seeing a cooling system you can trust. When you’re running a MerCruiser inboard or sterndrive with closed cooling, you rely on that system to keep temperatures steady whether you’re idling through the no-wake zone or pushing hard across open water. Mercury’s 877770K1 Extended Life Coolant delivers that peace of mind. It protects the engine you depend on, keeps scale from building up, and maintains consistent temperatures without you having to think twice. It’s one of those behind-the-scenes essentials that makes your whole boating season feel smoother.

Key Features

• Formulated for all MerCruiser closed-cooling gasoline engines
• Pre-diluted 50/50 mix with de-ionized water
• Provides up to 5 years or 1,000 operating hours of protection
• Ethylene glycol based for reliable freeze and boil-over protection
• Offers freeze protection down to –34°F and boiling protection up to 265°F
• Will not cause coolant gelling
• Meets ASTM D-3306 and D-4340 requirements

Engine & Boat Compatibility

• All MerCruiser gasoline engines with closed-cooling systems
• Sterndrive and inboard applications
• Ideal for cruisers, cabin boats, sport boats, tow boats, and larger runabouts

Performance & Practical Benefits

When you’re cruising on a hot day, the last thing you want is temperature creep or cooling issues. This coolant maintains a stable thermal environment, helping your engine operate smoothly even under heavier loads. The extended-life formulation reduces the buildup of deposits, helping water passages stay open and efficient. You’ll notice steadier gauge readings and fewer fluctuations during long runs.

Because it’s pre-mixed, there’s no measuring, guessing, or worrying about tap-water minerals getting into your system. You pour it in, and it’s instantly ready to protect. Whether you store your boat in cold climates or run hard in warm ones, the deep freeze and high-heat protection make a difference you can genuinely feel.

Why Buy OEM

With something as critical as cooling, shortcuts just aren’t worth it. Mercury’s extended life coolant is built around the operating needs of MerCruiser engines — not a generic automotive standard. That means better compatibility, better corrosion resistance, and fewer headaches down the road.

You get longer service intervals, cleaner internals, and a system that simply behaves the way it should. It’s the sort of practical choice every experienced boater makes when reliability matters more than anything else.

FAQ

Q1: What engines is this coolant designed for?

Any MerCruiser gasoline engine equipped with a closed-cooling system.

Q2: Can I mix it with traditional automotive coolant?

It’s technically compatible, but doing so reduces the extended-life benefits.

Q3: How do I know this is the right coolant for my boat?

If your MerCruiser uses closed cooling, this is the OEM-specified formula.

Q4: Does it work in extreme cold?

Yes — it protects down to –34°F.

Q5: Is it premixed and ready to use?

Yes, it’s a 50/50 pre-diluted blend with de-ionized water.