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BREAKDOWN! What To Do When Your Boat Overheats

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Boat On Fire

Have you noticed the temperatures seem to be going to extremes the last few years? Around the country, we have been seeing colder colds and hotter hots, and for those of us that play or work outside, extreme temperatures require extra precautions. And of course extra complaining! This time of year, I forget about the cold and complain about the heat (which I really should be happy about, because it means boating weather).

The extra heat can have a detrimental effect on the operation of our vehicles.  Years ago, I can remember running my ’74 Corvette convertible in local parades and running the heater to help dissipate the engine heat. I also have an air-cooled motorcycle that starts to run hot in too much stop-and-go traffic: not much airflow over the cylinders to keep the heat down. 

Not even boats are immune! If you have ever been out on the water and had an engine spewing steam from the engine compartment because it started overheating, well, you know what heat can do. In reality, it doesn’t matter if you have an air-cooled or water-cooled car, motorcycle or boat, it can overheat.

Overheating is no minor issue: according to BoatUS Marine Insurance data, 9 percent of boat fires are caused by engine overheating.

For boaters, how do you know when you’re running too hot, and what can you do about it?

How To Tell If Your Boat Is Overheating

Here are four pretty clear indicators that something is wrong:

1. The first and easiest is if the dash gauge for the temperature goes out of the green and into red.  

2. If it feels like the engine is losing power, you might be overheating. 

3. An overheated engine may not want to start up again after you shut it off, until it cools down.  

4. An unusually large amount of steam coming out of the exhaust. 

If your engine is running hot, you definitely have a problem that needs to be fixed. Troubleshooting and finding the problem can be difficult. A few of the more common issues include: 

-The water pump impeller has failed. 

-The engine belt driving the water pump is bad or broken.

-The engine raw water strainers are plugged. 

-Or maybe the grills or grates where the water is pulled into the cooling system is blocked or plugged.

A Crash-Course On Boat Engine Cooling Systems

The fact that your boat could overheat means you should know the basics of your engine cooling systems. 

The first type, full raw water systems (usually in older boats), pull the water you are in (lake, river, salt) into the engine’s cooling passageways in the engine, removing the heat from the engine by heating the water, and pumping the heated water back in to the lake (or ocean). Of course that also means anything in the water goes through the passageways: vegetation, debris, trash, etc. Therefore, blockage and damage to the pump can be an issue. Usually there are filters/strainers or screens to keep the particles out of the engine, but over time buildup can occur. That is why you should always flush your cooling systems.

Most new boats, however, have partial raw water systems. The engine is in a closed system that is very similar to your automobile, and contains antifreeze which actually keeps the water from freezing and raises the boiling point of the water slightly. Water passes through the engine and is heated. The hot water then passes through the heat exchanger (like a car’s radiator) and is cooled down before it returns to the engine. A car’s radiator has air passing through the radiator to cool the water. In a boat’s heat exchanger, water from the lake passes through the exchanger to remove the heat from the water in the engine. Make sense? Basically, cooling the engine relies on water being passed through something (radiator, exchangers) to remove the heat. If there is a breakdown in that process, the boat can overheat. 

What To Do If Your Boat Overheats

Okay, so now the big question is: what do you do if your boat is showing signs of overheating?  Well, it depends. If you are very far from a marina, you’ll need to cool the engine down before you can get the boat to a mechanic. The engine overheats typically when you’re headed from one place to another, so it’s not always the best time to pull into a cove and take a swim break! But that may be your best bet, to avoid having your entire day wrecked by a major engine failure. While the engine cools, here are some things to try…

-Check For Blockage. If you know where your raw water strainer is, check and see if it’s plugged. Also check for blockage in the “thru hulls” where the water is pulled in.  

-Check The Coolant. There are times when your cooling system needs some work, but isn’t in complete failure. If your boat uses a partially closed system (most new boats do), make sure you have coolant in the closed system. It is like checking the water level in a car. (Caution! Just like checking a car’s radiator, a hot engine means hot engine coolant, which means the coolant system will be under pressure when it’s hot. Wait for the system to cool down before opening it to check fluid levels.)

-Lighten The Load. You can try dumping the ballast water (or the beer cooler!) to reduce the weight of the boat. Anything that puts a load on the engine increases the heat it produces, and if your system is slightly compromised, a heavy load can make it overheat.

-Air It Out. Some people believe they can open the engine compartment and the increased airflow can help cool the engine. That’s an okay short-term way to help cool a hot engine, but it’s not a real fix. The engine should not overheat in the engine compartment: the boat is designed to operate with a closed compartment. Do make sure the engine area has lots of room around it (that’s why opening the engine cover can help, but should not be necessary). Also, running the blowers might help; blowers will remove some of the hot air from the engine compartment.

-If All Else Fails, Call For A Tow. If you have a nonfunctioning component in your cooling system, you might not make it back without damaging an engine, and should probably just call for a tow. The cooling system keeps the oil temperature down so the oil can lubricate the internal parts of the engine. Overheating ruins the lubrication and the metals parts start melting and sticking together. Or they just break apart with a big bang. Neither of those things are good. So if the engine cools down but heats right back up when you restart it, you should probably get a tow to shore, which is probably cheaper than a new engine.

Lake Tow

An Ounce Of Prevention

So it’s clear that if your boat is overheating, there is not one great solution. As with so many things mechanical, your best bet is to perform regular maintenance:

-On the cooling systems, make sure the strainers and systems are clean and flushed regularly. 

-Check the cooling hoses and fittings to make sure they do not leak and ensure the hoses are not stiff and brittle. 

-Tighten any loose clamps and replace corroded clamps. 

-Make sure you have the correct oil in the engine to manage the hot temperatures. Oil is the “lifeblood” of an engine. 

If you’re on the water and you overheat, make sure you stop quickly (and safely of course) and let it cool down slowly. I can tell you from first-hand experience that when a hose breaks, the engine can overheat. In my case it dropped steel valve seats out of the heads and jammed and bent the valves….oops! When that happens, you call for a tow.

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