Raw Water Cooled Engines in Saltwater

[VanBrudenship]

It is my understanding many marine engines are raw water cooled, diesel and gas. Many newer engines are closed systems. There are tons of older raw water cooled engines out there, yet I read that if you take a freshwater raw water cooled engines into salt water they will destroyed quickly?

Did manufacturers make freshwater and saltwater boats with jacketed engines and bare raw water engines? Or were they all made the same back then (70's/80's)?

When I asked my friend who is a marina manager in the PNW, he seemed puzzled about my precieved problem of taking a freshwater (Great Lakes) boat to the ocean.

I've googled and looked into this already without much clarification, I understand how the systems work but not as to their effect or common usage. Thank you.

 

[PierreR]

I live in the Great Lakes. I have seen very few raw water cooled systems here. Mostly outboards and few smaller I/O's

 

[VanBrudenship]

All the older 70's/80's inboard trawlers with gas engines that I've looked at are raw water cooled? In fact, a broker told me most are raw water cooled. Boats repowered into the mid 2010's are raw water cooled from what I've seen. We are talking inboards.

 

[Figment]

A lot of former sailors here will have memories of raw water cooled atomic-4 engines.
Yes they absolutely develop cooling issues over time as the water passages through the block become restricted by rust and mineral scale, but that's not at all the same thing as being "destroyed" by seawater.

Scaling-up to larger engines... the engines are the engines, there are no "jacketed" engines.

Adding a heat exchanger to turn a raw-water engine into a closed-system engine will take some time and money, but really shouldn't be all that complicated.

 

[PierreR]

All the older 70's/80's inboard trawlers with gas engines that I've looked at are raw water cooled? In fact, a broker told me most are raw water cooled. Boats repowered into the mid 2010's are raw water cooled from what I've seen. We are talking inboards.

Have you actually looked to make sure yourself. Many here think and engine is raw water cooled if it does not have a radiator.
You will probably find some inboards that are raw water cooled but most of them are trailerable. My definitions might be different than yours. Gasoline and inboard trawler don't belong in the same sentence.
Raw water cooled boats left in the water here would not last that long either. Even with anodes.

 

[VanBrudenship]

Pierre, we are talking about 30-35 ft boats. Tollycraft, Trojan (debate if trawler or convertable, makes no difference it's a nomer). Not trailerable without permits. A boat with a radiator? What? Do you mean heat exchanger and oil cooler? Ex. Chrysler 318 and 360 engines were raw water cooled; and many were put in larger boats as twins.

 

[VanBrudenship]

Let's narrow this down and get back to the original question. Many people have raw water cooled engines that they run in the ocean. Knowing additional maintenance will be required, and replacement of parts (manifold for one) is this a significant problem?

 

[av8r]

I’ve run gas-powered 225 and 300 hp Mercruiser engines in salt water, but they were not raw-water cooled. They were cooled by running ocean water through heat exchangers and exhaust manifolds, which cooled the engine coolant (“antifreeze”) and the exhaust gas flow.
The exhaust manifolds should be considered replacement items with a 5-7 year lifespan, it’s a good idea to pressure test the heat exchangers regularly.

 

[rslifkin]

Older gas engines are frequently raw water cooled, but some do have closed cooling (mine included). Outside of some older small sailboat diesels, most diesels have closed cooling.

Personally, I'm no fan of raw water cooling even in fresh water. It forces you to run engines colder than optimal just to reduce buildup in the cooling systems and it's generally more of a pain to deal with in my experience.

 

[SteveK]

Yes, if salt water is used in the body of the engine as coolant the engine will fail sooner and cannot be rebuilt than the same engine that has fresh water coolant with heat exchangers, Salt water is corrosive.
Outboards can be flushed after use as can an inboard to avoid this.

 

[PierreR]

I have boated the great lakes for 60 years. I have not run into any raw water cooled since the early 70's Raw water cooled means there is lake water circulating around the pistons and in the heads. instead of antifreeze around the pistons, around the heads and in half of the heat exchanger with raw water in the other half of the head exchanger and injected into the tail end of the exhaust manifolds and out the exhaust.

 

[PierreR]

Let's narrow this down and get back to the original question. Many people have raw water cooled engines that they run in the ocean. Knowing additional maintenance will be required, and replacement of parts (manifold for one) is this a significant problem?

If they are raw water cooled, YES, that is a significant problem and even in fresh water of the Great Lakes will not last long. 10-15 years but in that time likely to have freeze busted due to one little mistake along the way.