Help me understand how my motor cooling system works

[alexar]

My 93 sundancer with a 5.7 and alpha 1 has a sticker that says "freshwater cooled" on a pressurized tank (with a radiator cap) that is on the front of the block.

I was told that coolant surrounds the block and goes through a heat exchanger that is cooled with water from outside, which all sounds good but I don't know where water is coming in from.

The only water inlet that I can find is on the outdrive. Does that pull seawater into the risers and then out?

 

[Bill Curtis]

You sound pretty new to the boating thing.

"Freshwater Cooled" is a very good thing if properly maintained. My 220 has a 454 Magnum with closed cooling, so let me try to break it down in the simplest version I can.

The "fresh water cooled" is actually what is called a closed cooling system. It works just like your car and that tank with the radiator cap is your heat exchanger (same as a "radiator"), except it uses water from outside and a pump to cool it, instead of air and a fan, like a car.

The liquid in the tank is automotive type antifreeze / coolant. It cools the engine, and maybe / maybe not the exhaust manifolds. NOT the exhaust risers that sit on top of the manifold and have the 4" hoses on them, as that is where the raw water exits the boat, through the exhaust.

The outside (raw) water is sucked in thru the outdrive unit by a pump , in your case is an Alpha, so pump is inside drive unit.
That raw water is circulated through a couple of coolers, like power steering and oil coolers, then into the heat exchanger to cool the antifreeze, then out through the exhaust. Pretty simple and robust system.

Since you are new, the very best thing you should have, next to tools and a life jacket, is the OEM service manuals for the engine and outdrive. I happen to have them in PDF and can give you a link to download them to your PC. Let me know

Curtis Out

 

[Bill Curtis]

Here a simple closed cooling diagram. Ignore the "Bravo" thing as that basically signifies, as far as cooling is concerned, a belt driven raw water pump attached to engine, not like an Alpha internal raw water pump.

 

[alexar]

Thank you, that's what I'm looking for. I have a friend with the same boat and he has a water pickup on the underside of his boat for the raw water.

Having those downloadable manuals would be great. I have lots of automotive engine experience but less with marine motors.

 

[Bill Curtis]

Alex, sent you a PM.

Just remember, these are just Chebby engines with some marine specific modifications.

Guess your friend has a Bravo Drive on it with the water pump on the engine.

 

[alexar]

Thank you Bill!