A Complete Guide to Jet Ski Cooling Systems

Most riders don’t think about what happens under the seat until a warning light flashes or the engine cuts out. But understanding how your personal watercraft (PWC) stays cool is essential for longevity and performance. Just like a car, a jet ski engine generates immense heat. Without an effective way to dissipate that heat, the engine would seize in minutes.

However, unlike cars, jet skis operate in a unique environment. They have an endless supply of water right beneath the hull, which changes how engineers approach cooling. Whether you ride a Sea-Doo, Yamaha, or Kawasaki, the cooling system plays a critical role in keeping you on the water doing what you love most. Explore SBT’s complete guide to jet ski cooling systems to learn a little more about maintaining it.

How Does a Jet Ski Cooking System Work?

At its core, a jet ski cooling system manages engine temperature by transferring heat away from the engine block and exhaust components. The process typically involves circulating water around the cylinders and through the exhaust manifold.

Water absorbs the heat generated during combustion. The system then expels this heated water back into the body of water, or cycles it through a heat exchanger, depending on the design. The goal remains consistent across all models: maintain an optimal operating temperature to prevent overheating and sustain peak performance.

What Is an Open-Loop Cooling System?

An open-loop cooling system is the most common design found in older models and many modern Yamaha and Kawasaki skis. This design draws water directly from the surrounding body of water.

The jet pump pushes water through intake lines and circulates it directly through the engine’s cooling jackets and exhaust system. After the water absorbs the heat, the system flushes it out through the exhaust.

The primary advantage here is simplicity. There are fewer parts to break, and the water source is infinite. However, this design exposes the engine’s internal passages to whatever is in the water—salt, sand, algae, and debris. Over time, this causes corrosion and blockages, especially for saltwater riders.

What Is a Closed-Loop Cooling System?

Sea-Doo popularized the closed-loop cooling system (CLCS), which functions much like a car’s radiator system. In this design, the engine circulates a dedicated coolant (antifreeze) through the engine block.

Instead of an air-cooled radiator, the system uses a ride plate which acts as a heat exchanger. As the hull moves through the water, the cool water outside absorbs heat from the ride plate, cooling the antifreeze circulating inside.

Why Is Flushing the Cooling System Important?

Flushing removes contaminants that accumulate inside the cooling passages. Saltwater is the biggest enemy, as it crystallizes when it dries, creates blockages, and eats away at aluminum components. Even freshwater riders pick up sand, mud, and aquatic weeds.

You should flush the system after every ride in saltwater and periodically when riding in fresh water. Most modern skis feature a convenient hose adapter. You simply connect a garden hose, start the engine, turn on the water, and let it run for the manufacturer-specified time—usually 90 seconds to two minutes. Always start the engine before turning on the water to prevent hydro-locking.

What Are the Symptoms of a Cooling System Failure?

Identifying a problem early saves thousands of dollars in repairs. The most obvious sign is an overheating warning light or buzzer on the dashboard. If this happens, stop the engine immediately.

Other symptoms often include:

• Steam Coming From the Engine Compartment: This suggests a leak or a lack of water flow.
• Loss of Power: The engine’s computer may enter limp mode to protect itself.
• Hot Smell: A distinct odor of burning rubber or hot metal often precedes mechanical failure.
• Dry Exhaust: Water should exit with the exhaust gases. If the tell-tale pisser (a small stream of water on the side of the hull) is dry, water isn’t circulating.

How Do You Maintain the Intake Screen?

The intake grate is the first line of defense. It prevents large rocks and debris from entering the jet pump and cooling lines. If weeds or a plastic bag clog the grate, water flow stops, and the engine overheats rapidly.

Inspect the intake grate before and after every ride. If you ride in shallow water, check it frequently. Clearing debris immediately prevents starvation of the cooling system. If you notice frequent clogging, consider upgrading to an aftermarket intake grate designed for your specific riding conditions.

Can You Upgrade a Jet Ski Cooling System?

Yes, performance enthusiasts often upgrade their cooling systems. Stock systems handle stock power levels, but once you tune the ECU or add a supercharger, the engine generates more heat than the factory system can handle.

Upgrades might include the following elements:

• Additional Cooling Lines: Increasing water volume to the engine.
• High-Flow Fittings: Reducing restriction in the lines.
• Upgraded Intercoolers: Cooling the intake air more efficiently for better combustion.

When pushing an engine beyond factory specs, installing high-quality aftermarket jet ski parts becomes necessary to handle the increased thermal load and maintain reliability. Partner with SBT to get the parts and accessories you need to get the job done right.

How Does Winterization Protect the Cooling System?

Freezing temperatures destroy engines. Water expands when it freezes, and if water remains inside the cooling jackets or exhaust manifold, it will crack the metal casting.

Winterization involves draining all water from the system and replacing it with nontoxic RV antifreeze (for open-loop systems) or ensuring the coolant mix is sufficient (for closed-loop systems). You must run the antifreeze through the system until it exits the exhaust, ensuring it displaces all raw water. This simple step prevents catastrophic damage during the off-season.

How Do You Troubleshoot a Clogged Cooling Line?

If the engine runs hot but the intake is clear, a blockage likely exists inside a hose or fitting. Sand is a common culprit.

Start by disconnecting the cooling lines at the entry and exit points. Use compressed air (at low pressure) or a garden hose to backflush the lines. Work backward from the exit point to push debris out the way it came in.

Next Steps for Jet Ski Maintenance

Keeping this guide to jet ski cooling systems handy can help you take control of PWC ownership with ease. Whether you rely on an open-loop system for its simplicity or a closed-loop system for saltwater protection, the principles of maintenance remain the same.

Keep the water flowing, keep the debris out, and flush the system religiously. If you suspect an issue, address it before your next ride. A cool engine is a happy engine, and a happy engine means more time on the water. Remember to partner with SBT to get various parts for your vessel.