Fresh or sea water cooling for a 5411 diesel engine

[2xcrash]

I’ve got a 1982 30’ Catalina with a 5411 Diesel engine. My sailing is only going to be local cruses of 3-5 hours, Redondo beach to Catalina or just local day trips.
It’s set up as sea water cooled and I’m due to change the water impeller and was wondering if I should start thinking about putting a fresh water exchanger in it? She never has over heated. I don’t think I’ve seen her get above 120.
Want to start putting smart money into the boat before I need to fix something cause it broke.

What’s your opinion

[Hoosierdoc]

Just curious. If the 36 year-old system has been working well, why consider changing it?

[GordMay]

Universal 5411 Diesel Shop Manual ☞ https://www.westerbeke.com/technical...hnical_man.pdf

[2xcrash]

Originally Posted by Hoosierdoc

Just curious. If the 36 year-old system has been working well, why consider changing it?

Well I guess cause over 36 years they’ve made improvements on a thing or two.

It’s the reason I ask the question. Is there benefits, are they worth it and if I was going to invest in improving my boat is this a worthy investment.

I’m from the school of “there’s no dumb questions “ so I ask a lot of them.

[Hoosierdoc]

I agree on the questions, that’s why I asked mine too. I’m a novice with no advice to offer as to your question, more curious as to why one would change systems if it’s working ok. Wasn’t Sure if you could recapture the heat for other purposes with a fresh water system.

[Lepke]

It's always better to have fresh water cooling. Eventually all salt water cooled engines have a cooling passage rust thru if the engine lives to old age. I've seen it in a hundred engines. Usually lake and river boats used on the ocean.

I've changed about a dozen over for other people. If money's tight, good used heat exchangers can be found on ebay. Some replacement heat exchanger makers have kits for common engines.

On fresh water cooling, the engine can be run at a higher temperature. Usually from about 140° to 180°. Some diesels run better at about 200° and get better mileage.

[2xcrash]

I didn't post it but like clock work my water passage plugged. I'm glad I wasn't out and about. Now I'm looking to unplug it. After I get this cleared Ill be looking to add a exchanger.
And thanks for the diagrams! I've been looking for them for a while.

[RaymondR]

Provided you are diligent in keeping good anodes in the engine it will probably outlast the rest of the boat.

The reason so many engines have a heat exchanger fitted these days is the the cooling water circuit in the engine has parts fabricated from alloys which will act as an anode to the cast iron block and rapidly corrode in the presence of sea, or even fresh water.

Most marine engines these days are adapted from transport or industrial diesels rather than specifically designed for marine use.

[Compass790]

Originally Posted by 2xcrash

I’ve got a 1982 30’ Catalina with a 5411 Diesel engine. My sailing is only going to be local cruses of 3-5 hours, Redondo beach to Catalina or just local day trips.
It’s set up as sea water cooled and I’m due to change the water impeller and was wondering if I should start thinking about putting a fresh water exchanger in it? She never has over heated. I don’t think I’ve seen her get above 120.
Want to start putting smart money into the boat before I need to fix something cause it broke.

What’s your opinion

We have a 1980 raw water cooled engine & it has very little corrosion internally. I did consider converting it to fresh water cooled but decided against it as I can see it lasting another 39 years easily as long as you keep up with the anodes. I'd rather spend the money on beer.
As Lepke said running at a higher temp that you would get with fresh water cooling is slightly more efficient but would be a long payback time I'm guessing.
You have more failure points adding another water pump & heat exchanger.
We did put a tee in the raw water intake & flush with fresh water when we get back to the marina so salt water doesn't sit in block.
If you dont do that you need to descale occaisionally but you'd need to descale a heat exchanger too.
For your usage I can't see it being worth it but just my 2c worth

[2xcrash]

Originally Posted by Compass790

We have a 1980 raw water cooled engine & it has very little corrosion internally. I did consider converting it to fresh water cooled but decided against it as I can see it lasting another 39 years easily as long as you keep up with the anodes. I'd rather spend the money on beer.
As Lepke said running at a higher temp that you would get with fresh water cooling is slightly more efficient but would be a long payback time I'm guessing.
You have more failure points adding another water pump & heat exchanger.
We did put a tee in the raw water intake & flush with fresh water when we get back to the marina so salt water doesn't sit in block.
If you don't do that you need to descale occasionally but you'd need to descale a heat exchanger too.
For your usage I can't see it being worth it but just my 2c worth

So I got everything cleared. If I close of the return line to the mixing T and removed the Thermostat water flows right on out the back.
Now Ive got everything back to normal and its spitting out the back but intermittently. I haven't had a chance to run it for long cause I had to go to work. Here are my ???'S

How much and how often should the water be spitting out the exhaust.

I look at my buddies boat and its spitting out regularly but he has a fresh water system. So I understand that the water is constantly flowing through exchanger.
The raw water cooling system circulates until the thermostat opens and then water flows back out the exhaust. So I wouldn't see a regular stream out the back right?

How much should I see come out the back?

[Wotname]

Originally Posted by 2xcrash

....
The raw water cooling system circulates until the thermostat opens and then water flows back out the exhaust. So I wouldn't see a regular stream out the back right?

How much should I see come out the back?

No, this is not how a raw water cooling (RWC) system works. In a RWC engine, when cold the thermostat directs almost all the water direct to the exhaust mixing point until the engine comes up to temperature at which point, the thermostat allows some more water though the block and then to the exhaust mixing point. The RWC thermostat acts as a sort of two way valve rather than just a restriction like in a standard coolant system.

Thus the amount of water exiting the exhaust remains the same regardless of engine temperature.

[2xcrash]

[QUOTE= The RWC thermostat acts as a sort of two way valve rather than just a restriction like in a standard coolant system.

Thus the amount of water exiting the exhaust remains the same regardless of engine temperature.[/QUOTE]

Right so if the valve is closed the water diverts to the water inlet. It's not until that valve warms up and opens up that it would be diverted overboard.

I don't understand what I'm missing.

I work in an oil refinery and understand pipelines,exchangers and pumps really well. Just on a grander scale.

When I'm on the motor when everything was working well I didn't put out a lot of water overboard but now I'll go almost 45 seconds till some spits out.

[Wotname]

Originally Posted by 2xcrash

Right so if the valve is closed the water diverts to the water inlet. It's not until that valve warms up and opens up that it would be diverted overboard.

I don't understand what I'm missing.

I work in an oil refinery and understand pipelines,exchangers and pumps really well. Just on a grander scale.

When I'm on the motor when everything was working well I didn't put out a lot of water overboard but now I'll go almost 45 seconds till some spits out.

This is a typical RWC circuit (in this case it's a Yanmar 1GM10).

When the thermostat is cold, it prevents water passing though the block and head and allows water to pass though the bypass hose.

When the thermostat is hot, the opposite occurs i.e. it allows water to travel though the head and block and prevents water to travel though the bypass hose.

Thus at all times, the amount water entering the exhaust system remains the same.

[JimsCAL]

My previous boat had a raw water cooled 5411. The 5411 is a marinized Kubota industrial engine and really should never be run on raw salt water. I had to replace my engine with a rebuilt one before I sold it 10 years ago due to corrosion (water in oil). Prior to that I had lots of problems with plugged cooling passages in the engine and overheating. I strongly suggest converting to fresh water cooling. One way would be to use one of the kits sold by Moyer Marine and Indigo for the Atomic 4 engine.

As to the water flow in the exhaust, it varies widely depending on the engine temperature. When cold, the cooling water is recirculated, and only a small amount goes out the exhaust. As the temperature comes up, the thermostat forces more water out the exhaust, and more raw water enters the cooling loop, maintaining the engine temperature. This is different than the "bypass" type systems found on many other raw water cooled engines that have a much greater water flow in the exhaust when cold.

[Wotname]

^^ JimsCAL, thanks for the explanation of the differences with the 5411 RWC. It helps me and I'm sure it helps the OP.