Top 7 Reasons Your Boat is Overheating & How to Fix It

Luckily we have only had to deal with this issue once aboard SV Sweet Ruca. We sucked up some Sargassum weed in the Bahamas. The problem was caught quickly as we showed a slightly above normal temperature reading. Having had this happen on other boats while transporting across the Gulf Stream, we thought we would share some tips to help those that haven’t encountered a boat motor overheating issue yet.

Top 7 Reasons Your Boat is Overheating & How to Fix It


There are many reasons why you could have an overheating problem on your boat. Here are a few reasons why your boat may be overheating and how to fix it:

1. Clogged Raw Water Strainer

The number one cause for overheating boat engines is a problem with the flow of water to the engine.

Most boats have a water strainer which catches harmful items before they can cause damage to your engine. Before you go searching under the water, for a problem, check your boats water strainer by unscrewing it and cleaning it’s screen. 

How-to fix: The water strainer is usually located close to the water intake, just follow the hose that goes from your water pump to the bottom of the hull. If your boat doesn’t have a strainer, or is outboard driven such as popular bass fishing boats and center consoles, don’t fret, there is still another place to look.

2. Overheating Due to Debris in the Intake

Weeds and plastic bags are almost always the first thing to check for when you hear the dreaded beeping or your temperature gauge goes into the red. As the boat’s water pump creates a hefty amount of suction, it is easy for debris to be sucked into and clog the raw water intake. Growth of sealife while the boat is at anchor can also clog water intakes.

How-to fix: To solve this, lift the stern drive or outboards and check to see if the little grate where the water goes in is all clear. For sailboats, inboards, and jet-skis, this may require a jump into the water to clear the water intakes.

Anytime you are working with the engines or entering the water, be sure to make sure the boat is turned off and the key is out. If entering the water, check your surroundings and water temperature. Only do so if it is safe, otherwise call a professional.

3. Failed Impeller

The next most popular culprit which cases boat overheating is wear and tear or failure of the water pumps impeller. Most sailboats and powerboats, and even outboard boats, have a pump which feeds the engine water. Inside this pump is a small rubber impeller. Think of a paddle wheel, that is what it looks like. As it spins it sends cool water on to your engine.

Over time the rubber raw water pump impeller degrades, or can be damaged by debris in the water. It should be inspected often, and replaced as needed. For many boats this is done during annual service work.

How-to fix: Keep a spare on board, as they can usually be changed out with basic hand tools. An impeller puller is the proper tool, but most times it can be swapped with pliers and a screw driver. 

4. Secondary Water Pump

Some boats, like cars, have a cooling system that not only uses sea-water to cool the engine, but also use antifreeze or coolant in a separate cooling system. This is called closed loop cooling, and it is usually used on larger boats with more complex engines.

Like a car, these engines utilize a secondary water pump driven by a belt or gear on the motor. These can fail internally over time or from lack of maintenance.

How-to fix: Replace or rebuild the pump.

5. A Bad Belt

Also like a car, a secondary water pump relies on a belt to power it. Look on the front of your engine, sometimes under a protective cover, for a black belt. Like an impeller, these wear over time or when they are out of adjustment. 

You may hear some noise or see black dust in your engine compartment if your belt is failing. Make sure to check this item regularly and include it in your maintenance schedule. 

How-to fix: It is also a good idea to keep a belt for your engine handy as a spare. Make sure you tension the belt properly. 

5. External Temperatures

Outside air and water temperatures have an effect on your boat engines operating temperature. 

How-to fix: Slow down for a bit and lessen the load. Turn on your boats blowers.

When the air is very hot, or the water is very warm, make sure to be conservative in your boat’s operation until you know the effects it is having on your engine’s operating temperature.

6. Blower Failure

Many boats engine compartments don’t have great airflow. To keep temperatures in check, additional air is provided by electrical blowers. These blowers are essentially cooling fans which pull air in from the outside and circulate it around the engine compartment.

Excess heat build up in the engine compartment can have catastrophic effects on electronics, batteries, wires, and hoses. Check to make sure your blower is working before you start the engine.

How-to fix: Possibly, if it is safe to do so, open a hatch for additional ventilation. Check electrical connections and fuses. Repair or replace blower.

7. Internal Engine Issues

Last but certainly not least, an internal engine issue could be causing the problem. This is something no boater wants, and usually requires the help of a professional to fix. Frequent maintenance can help prevent expensive problems such as corroded heat exchangers, failed gaskets, or clogged exhaust elbows from happening.

How-to fix: Get some tools and delve deep into a shop manual, or if DIY isn’t your thing, it’s time to seek the help of a mechanic.

What else could be causing your boat overheating issue?


Check to make sure you have the proper amount and type of oil and fuel in your boat. Ensure the spark plugs are the proper part number. Don’t run your boat past it’s designed capacity limits or attempt to tow other vessels. Check for proper exhaust and exhaust water flow. 

Want to read more about overheating boat motors? Here is a link to the topic at Boat US:

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