Raw Salt Water Cooling

[Red Rider]

I was talking with a friend about his project boat. He is powering it with a 350 SBC driving a Jet Pump, and is planning on using raw salt water for cooling. The only thing special he is planning on doing is putting a "Salt Water" water pump on on the engine. This pump has a bronze impellor and Stainless Steel shaft/plate????????? And the exhaust is aluminum with aluminum water jackets. (He says he will also use zincs on the boat).My question is what kind of life can he expect before the block, heads or something rust through from the salt water. 6mos? 1 year? 2 years? 3 years? It will last forever?I think he should just use a heat exchanger, tap the Jet Pump for water to run through the heat exchanger and then through the water jackets on the exhaust. He disagrees, as he doesn't want to lose speed (thrust) from the Jet Pump, and he wants to keep everything simple. He think he will get several years of life from it before he has to replace the engine. As he says small block chevy engines are cheap, and he has about a ½ dozen sitting in his shop.

[Walt T]

Most engines will wear out or be damaged from something else before they rust through in the block and heads. If it is flushed religiously then he can expect longer life. Eventually he will have plugged cooling passages and will have overheating problems. That's they way it is with salt water cooled engines and there are lots of them out there. Keep the engine temperature below 150 degrees in salt water. Leave him alone and hope he takes you for rides.

[DJ]

Agree with DW. Heat is the catalyst in salt water.Typically, the engines break long before they have corrosion problems (except manifolds and risers).

[Red Rider]

The exhaust manifold and risers are aluminum, how bad do you think the salt water will affect them? I don't know what type of aluminum but they are "GALE BANKS" brand.

[f_inscreenname]

Do a search on here to see what he needs to change for salt water use. Like brass freeze plugs and a marine thermostat just to name a few. Any marine exhaust is made for salt water.

[DJ]

Red Rider,The salt water will eat those two. In some cases, risers/manifolds are almost considered "sacrificial".

[f_inscreenname]

I to should have said they all go bad eventually . Some sooner then later but I have a friend that has aluminum exhaust (raw water cooled) that is original to the boat (17Â’ 1972 Scottie Craft). You can do the math. The only time I have ever seen a (flushing) hose hooked up to his boat is when he is de-winterizing it.

[rodbolt]

hello yep change the freeze plugs, the original head gaskets may or may not last very long, the aluminium risers in salt water will dissapear fairly rapidly in salt. but if he has spares just buy the cool refreshing beverages and enjoy the rides good luck and keep posting

[akriverrat]

the thrust loss from using the jet pump for cooling is so small that it can't be measured in real life. not having a seperate cooling pump is one of the major advantages of jets. the aluminum manifolds should be good for at least 10 years if they don't get freeze damaged and he doesn't put in any steel fittings. they last much longer than cast iron in saltwater. instead of putting a seperate cooling pump he should spend his money on a fresh water cooling system. on a block only system all that is needed is the cooler and mounting brackets and some hose. will probably be cheaper than the marine gaskets, freeze plugs,and cooling pump. it will extend the engine life and increase the effeciency. aluminum intake manifolds will rot fairly quickly in a rwc motor being in direct contact with the cast iron block. not a problem with fwc. when he assembles the impellers to the pump be sure the shaft, keys, and bearing sleaves are greased with a good quality marine grease.it is a good idea to dis-assemble and regrease at least every second year. DO NOT use any copper based anti-sieze or bottom paint. he will regret it if he does. if it is an aluminum hull one or two 3 by 4 inch zincs on the hull should be plenty if the one on the pump is kept in good shape. not many pumps are actually designed for salt water use and if the boat isn't trailered it should be serviced at least once a season. watch out for the seaweed and plastic. you can run over anything else. i only check the charts when i am looking for the halibut hole. if i cant see it i drive over it.

[Red Rider]

Everybody thanks for all the responses. We talked over everyones answers and are going to go with a freshwater/antifreeze closed cooling system for the engine and the exhaust manifolds. From the risers back will be raw water. Water for cooling the risers will come from the jet pump. We haven't decided on a hull mounted heat exchanger or one using raw saltwater supplied by the jet.