Raw Water Cooled Engines in Saltwater

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
V

VanBrudenship

Veteran Member
Joined
Jan 19, 2022
Messages
43
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.
 
I live in the Great Lakes. I have seen very few raw water cooled systems here. Mostly outboards and few smaller I/O's
 
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.
 
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.
 
VanBrudenship said:
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.
Click to expand...
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.
 
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.
 
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?
 
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.
 
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.
 
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.
 
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.
 
VanBrudenship said:
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?
Click to expand...
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.
 
PierreR said:
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.
Click to expand...
There are many boats that still have the original engines that are raw water cooled in the Great Lakes area??? That are 40 or 50 years old??? What is corrosive about fresh water, I have no idea what you are talking about. Saltwater, of course, Fresh? Maybe the brokers and owners I am talking to are all BS'ing me or the alternative....
 
VanBrudenship said:
There are many boats that still have the original engines that are raw water cooled in the Great Lakes area??? That are 40 or 50 years old??? What is corrosive about fresh water, I have no idea what you are talking about. Saltwater, of course, Fresh? Maybe the brokers and owners I am talking to are all BS'ing me or the alternative....
Click to expand...
You have question marks by Great Lakes All of the ones I encountered were wood boats built in the 50's and 60's and did not last long. Freeze breaks during storage was a very common problem and still is even with heat exchanger cooled engines.
It's easy to be fooled looking at engines. Most engine heat exchangers are built to look like part of the engine. If the engine has a radiator cap and you open it and see liquid inside you are looking at the heat exchanger, not part of the engine.
Any water with minerals in it that has oxygen is corrosive, as in, rust. This is accelerated with heat around the engine and most of it takes place during operation and after shut down.
I would wager that finding and ignorant broker is far more likely than finding a gasoline inboard raw water cooled engine is a 30+ foot boat on the Great Lakes.
I hire nothing done on my boat. There is nothing I can't fix and still do. That is because there is no shortage of ignorance in service and sales people.
 
VanBrudenship said:
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?
Click to expand...
I grew up on salt water. All the engines of the boats we had were raw water cooled. They seemed to last forever. Of course "forever" meant something different as a kid. The engines did need to be descaled periodically as part of the normal maintenance. Those folks that routinely did a fresh water flush after every use had much fewer problems than those that didn't.

If you are talking to brokers on the great lakes, they likely have no direct knowledge or experience with operating boats in salt water. Old engines are still old engines and nothing will last forever, but a raw water cooled engine won't be "destroyed quickly" if moved to sea water.
 
dhays said:
If you are talking to brokers on the great lakes, they likely have no direct knowledge or experience with operating boats in salt water. Old engines are still old engines and nothing will last forever, but a raw water cooled engine won't be "destroyed quickly" if moved to sea water.
Click to expand...
Good point. A lot of great lakes boaters act like a single drop of salt water will instantly destroy any boat. Most people around here are shocked to find out that my boat spent 33 years in salt water.
 
The old Chrysler and Crusader gassers seemed to do okay even in salt water. There are a lot of failure points beyond raw water cooling on these older boats so many have long since gone to their grave. My impression is raw water cooling was displaced by fresh water cooling about the same time that wood was displayed by fiberglass. Given the cost of slips on popular boating venues such as PNW and California, hard to justify owning a gas/wood boat. Warm water venues such as Florida accelerate deterioration of all boat components so they are rare for other reasons.

From a distance, seems like the inland lakes and waterways are the only places where there is even a market for gas, wood, and/or raw water yachts of any size. Taking them elsewhere will accelerate their demise, but not short fuse.

Peter
 
Wonder if this is the issue can be solved by decommissioning the raw water ingress and exhaust. Use a keel cooler with a pump. Now coolant running through the engine. Combustion gasses still need to be dealt with but that’s another matter. Know of a local commercial lobsterman who told me he used reconditioned car engines with a home brew keel cooler and dry stack. Found it was the cheapest way to go. Lost contact with him so don’t know if he just kept replacing the engine as needed. Think he put on huge hours as lobstering seemed to be his only source of income.
Know reverso makes an automatic fresh water flush for outboards. These are gas and commonly 300-450hp each. Hook up a garden hose and push one button. Will do up to four outboards like you see on big center consoles. Still only $1k for that size. Believe they make less expensive ones for single engine applications. Perhaps one of those would work for the OP. Personally find using a T or the after market cover for the strainer to fresh water flush is a hassle. Be nice if you didn’t need to crawl into the engine room to do it.
 
Last edited:
Raw water cooled engines can be converted to closed cooling with a heat exchanger as well, but the issue is the condition of the cooling system, block passages, etc. It takes thorough flushing before conversion and if it has seen salt, you may never get the system clean enough to avoid issues from bits of rust and such breaking loose, or deposits slowly dissolving and causing issues with coolant.
 
You must log in or register to reply here.

Similar threads

T
Location of anti-siphon valve in raw seawater cooling system
Replies
7
Views
810
TristanJ
T
PhilPB
FOR SALE: 1983 Mainship 34' MKlll - $32,000 - Palm Beach County, Fl
Replies
20
Views
2K
PhilPB
PhilPB
thead
Kadey Krogen 42PH
Replies
0
Views
1K
thead
thead
C
  • Locked
2003 Pacific Trawler 40 in turnkey condition, lying Bainbridge Island WA -- $224,000
Replies
9
Views
4K
CompuNerd
C
B
34' Pilot Mainship 2002 twin 4LHA STP 240hp 140000.00
Replies
0
Views
2K
BB-marine
B

Latest posts

Back
Top Bottom