Questions on cooling system function/ thermostat housing

Hey guys I have been getting into trying to repair things on my boat this time around. I find it fun and interesting learning how everything works especially with the help from you guys. I’m replacing my impeller and thermostat. Both have been removed already waiting for the replacement parts from bakesmarine.com should be here tomorrow. I tried following he hoses from the impeller to see where they go. So far from my understanding is the impeller drives the water from the bottom of the boat into the transmission/ v drive then through the impeller into the exhaust manifolds and motor does his sound correct? I noticed 2 screens on the underside of the boat I see one comes through the floor directly into a “livewell pump” I’m assuming for the ballasts and the other goes into a large water tube going into the transmission. That’s why I assumed it goes into the transmission first and at the last stage exits through he exhaust. If anyone could shed some light on if this is correct or if I’m mistaken.

Also the thermostat housing is extremely rusty inside is this normal? Picture included.

Thanks for all your help guys this forum rocks!

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You are correct the water pump sucks water up from the lake, through the transmission first and then through the oil cooler before entering into the engine (when the thermostat opens). Most of that water is also routed to each of the exhaust manifolds, which then exits with the exhaust.


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Pretty impressive that the impeller can pull water all that way especially if there is air in the lines. That’s the only thing feeding the whole system? Just that one little impeller driven by the belt and crank?

Yes. Because it is a positive displacement rotary vane impeller it doesn’t need priming and is quite good at providing water to the system at high pressure and volume. Don’t forget that their is also a second water pump in the system that is part of the normal water recirculating pump that all IC engines have. This is found mounted directly to the block of the engine. The second pump keeps the water moving throughout the engine, and cool water is supplemented as needed, as the thermostat opens and closes.

Very cool good to know. Thanks for the replies guys! When I go to install the thermostat is there a certain way it goes in I got a little hasty and pulled it out quick once housing was off. I know which way it goes as far as right side up but it’s not directional on any way is it? Also with my new impeller I received the new gasket but 2 o rings as well I don’t remember pulling any o rings. Is that for a different application?

As long as thermostat is the right side up, that’s all you need to do. Make sure to replace the gasket on the thermostat housing.

O-rings s not needed on our impeller pump style.


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