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1977 115HP How does the cooling system work?

N

nicklanigan

Contributing Member
Hi all, time for another of my queries regarding how these engines work... note I'm not trying to fix anything, but to increase my understanding.

I'm trying to get my head around how the water system works - I've just completed a rebuilt of the power head, so have intimate knowledge of how water circulates through the power head. The limit to my knowledge is the power head, which I lifted off what is known as the exhaust adapter, so haven't opened up the exhaust adapter or anything lower.

I get that water is forced upwards by the impeller, into presumably a water channel in the exhaust adapter. That channel routes the water to the thermostats and bypass relief valves. When cold, the relief valves vent the excess pressure, dumping water out of the motor. When the thermostats are opened by warm water, water flows upwards into the powerhead. Once water has traveled through the powerhead, it enters another channel in the exhaust adapter, presumably to be expelled via the prop?

Some queries -

Do I have the flows above correct?

Is there always some flow to the powerhead, even if the thermostats are closed?

What actually warms the water to the required temp to open the thermostats? It would seem it could only be the exhaust adapter heating up from either exhaust gases or from water that has already traveled through the power head. The water passing through the thermostats must always be freshly drawn water from the impeller as it has not yet traveled through the powerhead? Is there some kind of heat exchange going on, whereby the exhaust or spent water warms incoming water?

As always, appreciate people's time responding.

Nick.
 
Nick, you are missing one point: Water flows through the powerhead first, then is presented to the thermostats to see if it is warm enough. So the powerhead is what warms the water (or not). Yes, there is some flow even if the thermostats are closed. This is necessary in order to cool the exhaust system.
 
Thanks, fdrgator.

I'm confused about flows then. Does the water that's been through the powerhead heat the thermostat, which opens the route for cold intake water to start circulating? I guess in my head I assumed the thermostats were an inline device, ie. they were heated by the flow they sit in, and control that same flow, whereas it sounds like they are heated by the flow that has been through the engine, but controls the flow that has yet to reach the engine.
 
You got it backwards. They are heated by the engine and restrict (but not completely) the water leaving the engine if closed.
 
Thanks all.

Pulled the hoses from head to thermostat off just for my own confirmation.

Am happy to update my original post - the water flows upwards from the impeller, into the engine block via the exhaust adapter. This channel cannot be seen unless the powerhead is lifted off.

Water flows into the exhaust cooling area, water passage, and the heads. It then exits the heads and travels via the rubber hoses to the thermostats/relief valves.

I have also learnt that water then passes lower down, cooling the inner exhaust tube down to the prop exit. It is this water than can "spurt" from the two openings at the top of the exhaust section of the motor, along with exhaust gases at idle, rather than being ejected from the prop.
 
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