2002 4.3 Penta - Larson 180SEI

[Petefett]

New to owning a boat and this forum and looking for knowledge of how the raw water cooling system work/circulates. Bought this boat and restored the interior and love learning new DIY and curious on this aspect. I replaced the water pump recently and was curious how all of this flows through the engine to cool it and how it functions.

I figured out that water pulls in from the outdrive into the pump/impeller and up to the thermostat housing then out the 2 x 1 inch hoses to the manifolds. From there I'm looking for where it goes before exhaust or how its all routed.

Specific Questions:

What is the purpose of the "Circulation pump" part #3853850? There is a 2" hose part #3852288 that runs left side of this pump to the left side to thermostat housing part #3850360- What is its Purpose, function, etc? Next question related to that -Does this hose always have Hot Water running in it. I notice this hose is always hot water filled (very hot) and think it has something to so with telling the thermostat to open close? Or does this tell me I have something else needing replaced if that water is hot and not cool?

How can I tell if my Thermostat needs replaced and not working? Older boat so wondering if it was replaced

Overall manifolds stay cool, but notice the left side tends to be warmer than right. Is that normal?

Any advise or explanations are appreciated to this boat owner rookie. Tried to attach pictures but having issues.

 

[tpenfield]

You did not mention if you have 'closed cooling' (i.e. heat exchanger) or not. Assuming that it is not closed cooling . . .

The sea water pump brings in cool water from the outdrive as you mentioned. The circulating pump causes the water to circulate through the engine so that the cool water grabs the heat from the engine.

Water is expelled from the engine out to the exhaust as more water is brought in from the sea water pump. The incoming water essentially 'pushes' the same amount of water out of the engine to the exhaust where the water mixes with the exhaust gasses to provide further cooling. then the water ends back outside the boat . from where it originally came.

Also, the engine itself is a GM engine that Volvo-Penta sources from GM and then adds their 'stuff'. So, you may notice that the circulating pump looks just like what would go in a car/truck, with some minor differences.

 

[Petefett]

Thank you very helpful. Yes it’s not a closed system.

What about my question on the hose and thermostat?

Any advise there?

 

[Petefett]

[No message]

 

[tpenfield]

recirculating hose . . . it should go from the thermostat housing down to the circulating pump. The water circulates through the engine block via that hose. When the engine is cold, the thermostat is closed and very little water flows through that hose.

 

[Petefett]

Thank you, yes that is the hose I’m talking about. However question on when it’s running should that be hot water going through it? That’s the only one that’s hot. All others are cold to touch. I found a basic cooling diagram for a 5.0 penta and looks like the water flow says it should be cold water through that hose and not hot. Wondering if I have another issue going on or can the thermostat maybe shot and stuck open or closed so not circulating cold water. Thanks again. Don’t want to ruin the engine.

 

[tpenfield]

The water in that hose should be warm/hot It just came from the engine and some of it is about to go back into the engine again.

If you are still concerned, get an IR temperature gun, they are not expensive. You can then put some real temperature values to your engine's cooling system and know what is normal.