Diagnosing Outboard Overheating Problems

An outboard engine overheating is a serious problem that needs to be addressed immediately. However, sometimes the overheating issue is something as simple as a clogged component.

The cooling system in your outboard’s motor is what to look at if you’re experiencing overheating issues. An overheating engine is a problem that can’t be put off, since it leads to major problems that can do some expensive damage. Watch the video above or read on below to learn about several ways to diagnose an overheating outboard engine.


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Check the Water Output

Every outboard is a little different, but they all draw water in from the lower unit, and it gets pushed up into and around the powerhead by the water pump and then pushed out of the motor. The first area to check where water passes through the outboard is the water output (also known as the telltale).

Outboard overheating problems output

When water flows out of the output in a steady stream while you’re running the engine, it’s an indicator that water is at least flowing through the cooling system. Keep an eye on that if you don’t have a temperature gauge or indicator. If the flow is decreasing, it’s a sign that something deeper is going on in the motor. Inspect the output to make sure there isn’t a clog.

Check the Water Intake

On the other end is the water intake, which is a common cause of overheating problems. Water flows in through the intake, but so does any debris it picks up as the boat moves through water. 

Outboard overheating problems water intake

The intake has a small cover that prevents debris from moving up into the cooling system. However, it can get clogged up and keep water from getting up into the cooling system where it needs to go.

Check the Water Pump

If both the intake and output are clear, the next thing to check is the water pump, which sits at the top of the outboard’s lower unit. A bad water pump pushing water up to the powerhead may be causing the engine to overheat. 

Outboard overheating water pump impeller

To inspect the water pump, remove the lower unit on your outboard to access the pump. Inside the pump is a rubber impeller that’s driven by the drive shaft. An impeller’s rubber can get brittle and wear out over time, causing it to start breaking apart. If that happens, the broken impeller fins aren’t pushing water into the powerhead, and pieces of the impeller can cause obstructions deeper in the cooling system.

Check the Thermostat

If the water pump is in good shape, check out the thermostat, which controls how much water moves through the powerhead. When the thermostat fails in the closed position, it shuts off water flow through the motor. On the other hand, if the thermostat fails in the open position, it allows too much water to flow through the motor and prevent it from warming up. 

Outboard overheating problems thermostat

Unfortunately thermostats aren't made to be repaired, so if one fails, it needs to be replaced. Some outboards have more than one thermostat, so if one goes bad, it’s best to replace all of them at the same time since they tend to wear out in unison.

Outboard overheating thermostat

Check the Water Passages

If all else fails, check the water passages that run up to and around the powerhead for clogs. The way to prevent clogging in those areas is to flush the outboard after every use, especially if it runs in salt water.

Outboard overheating water passages

It takes a long time for that kind of buildup to happen on a newer outboard, but for an older unit that hasn’t been maintained properly, enough salt and gunk can accumulate in there to slow down or stop water flow. And the more this area clogs up, the harder it is to fix.

Outboard overheating cooling system

To prevent outboard heating problems from happening, remember to flush the outboard after every use, and follow the manufacturer’s guidelines about replacing the water pump.


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