Many outboard owners do not realize the importance and function of the thermostat to their motor's lifespan and performance, however we can dig deeper to see that it plays a very important role with a number of functions..
What's the point and main role of the thermostats on my outboard?
The thermostat helps to ensure that the outboard operates at the correct running temperature, thereby achieving its best performance and fuel economy.
The main role is to regulate the flow of coolant coming into the motor based on the outboard’s temperature.
When the motor is cold, the thermostat remains closed. This will allow the outboard to warm up quickly at which point the thermostat will open up.
Unlike a motor vehicle engine, outboard motors do not use any coolant fluids in the motor. Raw water cooling is used on all outboards and many inboard/stern motor systems.
Due to there being no coolant in the outboard motor, there is no risk of any antifreeze liquid running out and mixing with the body of water being used for the boats operation, during the cooling process. Coolant is extremely toxic to wildlife, so this is a very important and meaningful reduction in environmental risk.
How Necessary is the thermostat to the outboard?
The thermostat regulates the temperature through the powerhead of the outboard. It provides a restrictor to ensure that water completely fills and circulates through the entire powerhead.
This is especially important for the top area as this is the part that absorbs the most heat from the cylinders and needs to be cooled thoroughly.
Without having a thermostat there is no restriction to the water flow, which will escape the path of least resistance and flow out the water exits of the outboard without filling and cooling the important top area.
This would cause the top of the head to receive less water for cooling, and as a result develop hot spots and early failures related to metal fatigue, motor corrosion and wear.
Testing and Finding the Thermostat
Generally the thermostat on an outboard is very accessible. Should it be needed, most vendors supply parts diagrams needed for identification and ordering spare parts if needed.
There is an easy manner for testing if your thermostat is opening and closing correctly. You can remove and place it in boiling water. The thermostat should open when placed in the boiling water and close again once removed.
Anti Freeze for winter storage
Certain pundits recommend flushing your motor with antifreeze prior to winter storage. This will prevent freeze damage to the outboard during a hard freeze,
While many owners simply drain the water from their outboard, by also flushing the outboard with antifreeze, you will prevent the residual water left over from turning into ice and causing damage during a hard freeze as well as prevent formation of rust within the cylinders.
The bleeding hole protection when flushing
Most modern four-stroke outboards have an orifice in the sealing surface referred to as a purge/bleed hole.
During Flushing maintenance this hole allows air to escape the engine block, and allows water to pass through the entire block, regardless of whether the thermostat is open or closed.
Most major outboard manufacturers have implemented the necessary safety features to ensure that the internals of your outboard are protected when flushing.
It is always important to follow your OEM manufacturers recommended instructions for flushing. This will ensure correct maintenance and longer engine life.
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