Volvo Penta 5.0Fi - Water pump question

[BradfromOH]

Hello all! Long time viewer and learner of this site, only second time posting a question.

I recently have moved on from the outboard world, and have just purchased my first sterndrive boat.

It's a 1996 Sunbird 200 Cuddy with a Volvo Penta 5.0Fi 50FAPNCA model engine.

My question relates to the water cooling system. I noticed that there is an actual water pump (Similar to a road car) in the center of the engine, however there is also a second water pump on the lower left hand side of the motor that also has its own pulley. When I look at the diagram shown on the marineengine . com website, it lists both of these as water pumps? (I would paste the link, but I dont think I am allowed to do so? Correct me if I can, I do not want to break guidelines).

I am a bit confused as the description lists both of these units as "water pump". Can someone explain to me what the difference of these two are?

Also, I tried searching for an existing topic of the procedure of replacing the impeller, but I was not able to locate a clear cut thread on how to do so, maybe I am searching with the wrong wording?

Thanks in advance for any assistance and of course, your patience with a newbie of inboard outboard.

 

[BradfromOH]

I just tried to upload a picture of the diagram, but I am not allowed to do so. Sorry...

 

[Maclin]

Welcome aboard!

There is the engine circulating pump like an automobile, that one circulates cooling water through the engine. There is raw water or sea water pump that draws in water from outside the boat thru the drive and supplies the cooling system, supplanting a traditional automotive type radiator. This raw water pump houses the impeller that is so important to keep alive so to speak, never let it run dry.

The raw water will run through the engine on demand, controlled by the thermostat which is in a different housing than the automobile equivalent. This housing is the traffic director for the raw water. There will always be more raw water than needed, and the rest is sent out the exhaust manifold into the risers and out the exhaust. This keeps the rubber exhaust hoses from melting.

There is a variant on the cooling system that is called Fresh Water cooling, using a heat exchanger with antifreeze coolant mix thru the engine, but there is still the raw water pump bring in the water that flows through the heat exchanger.

You should be able to find relevant posts on replacing the raw water pump impeller for your model and year of engine.

 

[bruceb58]

The raw water pump delivers a flow of water based on engine RPM to the thermostat housing. From there, the water goes to both the manifolds and the engine. All the circulating pump does is flow the water from the thermostat housing through the engine and back to the thermostat housing. The thermostat itself controls how much of this water circulates through the engine.

 

[Scott Danforth]

the impeller is in the raw water pump (belt driven, down low)

 

[BradfromOH]

Guys, thank you very much. Now that I have the actual terminology down I will search again for the impeller replacement how to. Be safe out there!