How Do Boat Engines Stay Cool?

Cooling systems in car and truck engines are all the same. Coolant is cycled through the engine block, heater core, water pump, and radiator, removing excess heat from the engine and preventing overheating.   

On the other hand, boats utilize two distinct types of cooling systems. In this article, we will go over how boat engines stay cool when you are out on the water!  

What Does the Cooling System Do?  

Internal combustion engines generate power with thousands of tiny explosions per minute, and all that combustion puts off lots of heat.   

With no place to go, all that heat would quickly lead to lots of issues, from a blown head gasket to catastrophic engine damage. Cooling systems solve this problem by cycling a liquid (antifreeze or water) through the engine block with a pump. The coolant absorbs heat from the motor, and then passes through a heat exchanger, allowing it to dissipate.  

While variations of this system are used across all internal combustion engines, there are some differences in the way boat motors are cooled.   

Raw Water Cooling  

Most small boats use a cooling system called raw water cooling. Unlike cars and trucks, boats operate in an unlimited supply of cold liquid, a lake or river! Raw water systems take advantage of this by continuously drawing water from the lake, pumping it through the engine, and expelling the hot water back out.   

A big advantage of raw water systems is simplicity. A rubber impeller pulls water from the lake or river, and expels it out through the exhaust. Raw water cooling is used on all outboard motors and many inboard/sterndrive systems.  

Without coolant on board, there is no risk of antifreeze leaking into the body of water a boat is on. This added benefit is a significant reduction in environmental risk, as coolant is extremely toxic to wildlife.  

Enclosed Cooling System  

In marine applications, an enclosed cooling system uses a combination of internally circulating coolant and raw water to keep the engine cool. Much like a car or truck, an engine with enclosed cooling has a reservoir of antifreeze that circulates through the engine. Unlike a car or truck, however, the coolant passes through a heat exchanger which is cooled by a separate raw water system instead of a radiator cooled by air.   

Enclosed cooling systems are more complicated than raw water but offer performance advantages. Enclosed cooling systems are more effective at cooling the engine, allowing it to operate at higher temperatures safely.   

Additionally, enclosed cooling is beneficial for boats operating in salt water. Keeping saltwater separate from the engine prevents corrosion and extends the life of the motor.   

Marine Engine Cooling Maintenance  

No matter what cooling system your boat has, regular maintenance is essential. If something goes wrong and your engine overheats, the repair bill can get expensive quickly. Raw water systems will require periodic impeller replacements and proper winterization every year to prevent cold weather damage.   

For boats with enclosed cooling, it is important to check and replace the raw water impeller if needed and make sure there is no buildup or corrosion preventing water flow in the heat exchangers. This is especially important for boats that operate in salt water, whether it is the ocean or the Great Salt Lake.   

Marine Service and Repair at Matson Point S  

Matson Point S is your go-to boat repair shop in the Salt Lake Valley. Our facility in Riverton is staffed with some of the most skilled marine technicians in Utah. You can trust our team to handle all your marine services, from general maintenance to diagnoses and parts replacement. Give us a call or schedule an appointment online today! 


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