Water is critical for a boat’s outboard motor to function properly. Water flows through the motor’s cooling system using a water pump and circulates throughout the powerhead before exiting through the exhaust system. Without it, an outboard motor will overheat. Overheating in outboard motors can be caused by any of various parts of the water cooling system. Vigilant regular maintenance on your outboard is your best insurance against a cooling system overheating problem.
Water Pump Failure
The most common cause of outboard motor overheating is water pump failure. Lack of raw water flow and lack of fresh water can cause water pump failure. Check for lack of raw water flow by noting the temperature of the outlet side of the system. A water flow problem is indicated if the water temperature is excessively high. Lack of fresh water can be noted if there is a large increase in temperature between the inlet and and outlet of the heat exchanger. Water pump failure can also be caused by a defective heat exchanger, though this is harder to check. Generally, if it is not a problem with lack of raw water flow or fresh water, the heat exchanger will be the cause.