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Old 02-04-2019, 10:16 AM   #1
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Modification on engine cooling system?

Hi, greetings from Tigre, Argentina!

I have a 55 Ft full displacement steel trawler with two GM 350 aspirated diesel engines.
The engine cooling is by means of heat exchangers + wet exhaust.
The system works ok at 50% of the engines power. At 80% or more, engines heat up.
I would like to change the cooling system to one of those used in fishing boats or commercial vessels: this is basically to attach a steel tube-serpentine to the outside of the hull, fill it with engine coolant system and eliminate the heat exchanger currently in operation.
Problem is I have no idea on where to get this information: already talked to a couple of mechanics, but their opinions difered a lot.
Anyone done the same before?
Please let me know your thoughts!
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Old 02-04-2019, 10:38 AM   #2
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Before you go to all that trouble and expense, have you checked out the current system you have now to see if it is working as designed?
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Old 02-04-2019, 10:41 AM   #3
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I have no advice to give on you cooling system design, but just wanted to say I have been to Tigre and it is beautiful.


Are your engines getting to the correct RPM at full throttle? If not, you may be over-propped which would cause the symptoms described.
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Old 02-04-2019, 11:34 AM   #4
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ND
Several bolt on keel coolers available to choose from, such as Fenstrum. You'd likely need a separate setup for each engine, not a small or easy task. As already noted by others, you need to determine why the engines are overheating.

Starting point would be a detailed description of engines, temperatures, marinization system and when the cooling system in it's entirety was last cleaned out. As mentioned, if over propped, the engines will overheat.

Is this a new to you vessel? Has it always overheated? how old are hoses? Are strainers clear and through hulls clean? Again, starting at basics should show why current overheat occurring.

Pictures would be helpful. Good luck and be patient.
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Old 02-04-2019, 11:42 AM   #5
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Before you go to all that trouble and expense, have you checked out the current system you have now to see if it is working as designed?
What you describe is common and usually repairable unless you know that it never worked. Have you inspected the inside of the system?
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Old 02-04-2019, 11:57 AM   #6
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I already did, several times.. but quite inefficient at high rpms
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Old 02-04-2019, 12:06 PM   #7
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Glad to know you were in Tigre.. if there is a next time, send me a PM and well se if we can arrange a tour on the boat!
About the engines: they are very basic diesels, and work pretty well... except for the tendency to overheat when I put some pressure on them.
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Old 02-04-2019, 12:21 PM   #8
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ND
Several bolt on keel coolers available to choose from, such as Fenstrum. You'd likely need a separate setup for each engine, not a small or easy task. As already noted by others, you need to determine why the engines are overheating. I have the feeling that the current heat exchangers were designed very close to their max limit and now, (being older) turned inefficient.

Starting point would be a detailed description of engines, temperatures, marinization system and when the cooling system in it's entirety was last cleaned out. As mentioned, if over propped, the engines will overheat.
Engines are 6 cil Bedford (GM) 350 cu inch manufactured in the late 80s in Argentina. They have been in use until the 90s in 5 ton trucks.
These are basically workhorses and work even under the worst conditions.

The operating temp of these engines is 70 C and after 30 min at 2800 RPM, they start getting temps near to 100 C.


Is this a new to you vessel? I bought this vessel (built 1985 or so) about 4 years ago, did an extreme overhaul during 3 years and use it trouble free (except for the heating issues) ever since.
I have no idea if the boat always overheated as the previous owner is a jerk and has no idea.



Has it always overheated? how old are hoses? All hoses new Are strainers clear and through hulls clean? Trough hulls completely clean Again, starting at basics should show why current overheat occurring.

Pictures would be helpful. Good luck and be patient.
Thank you!
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Old 02-04-2019, 12:27 PM   #9
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I wouldn't change to keel cooling until I understood what was happening with your raw water heat exchanger cooling. I know on DD 6.2 V8 diesels, air pockets can build up and block flow so there is a vent hose fix.


I would investigate those kinds of solutions first. Boatdiesel.com is a good place to post and get expert advice.


But here is some quick diagnostic info that you could gather and post. Get an IR temp gun and check the following temps:


1. Coolant temp in and out of the heat exchanger under moderate load when all is working ok.


2. Raw water temp in and out of heat exchanger as above.


3. Repeat the foregoing as it begins to overheat.


Post these values and we can help diagnose what is happening. Post the same to boatdiesel.


David
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Old 02-04-2019, 12:27 PM   #10
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Originally Posted by bayview View Post
What you describe is common and usually repairable unless you know that it never worked. Have you inspected the inside of the system?
Unfortunately there is no way of knowing if this system worked or not before I got the boat.
I know I will eventually find a solution to this, but would not like to "over react" and weld 500 meters of tubing to the hull.
From what I saw most of these designs are quite empirical... and work in most boats... other overheat
There must be a way of figuring out how to build such a serpentine type keel cooler
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Old 02-04-2019, 12:30 PM   #11
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Quote:
Originally Posted by djmarchand View Post
I wouldn't change to keel cooling until I understood what was happening with your raw water heat exchanger cooling. I know on DD 6.2 V8 diesels, air pockets can build up and block flow so there is a vent hose fix.


I would investigate those kinds of solutions first. Boatdiesel.com is a good place to post and get expert advice.


But here is some quick diagnostic info that you could gather and post. Get an IR temp gun and check the following temps:


1. Coolant temp in and out of the heat exchanger under moderate load when all is working ok.


2. Raw water temp in and out of heat exchanger as above.


3. Repeat the foregoing as it begins to overheat.


Post these values and we can help diagnose what is happening. Post the same to boatdiesel.


David
Great David!
At this very moment I am changing the gaskets from one of the exhaust manifolds , so, one engine is down.
As soon (perhaps this weekend) I have the boat in working order again I will follow your advise and post it here.

Best regards, Cosme
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Old 02-04-2019, 01:33 PM   #12
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When I was a fisherman many boats were still wood. Many had keel coolers, some homemade. The coolers were usually a couple of long copper tubes made into a loop and placed near the keel for protection. The front of the loop had a wedge to divert debris away from the tubing. The tubing is straight runs, parallel to the keel. Inside the hull there was a valve or a thermostat so only some of the water was sent thru the cooler when the engine was warming. Most had more than enough tubing for any sea water temperature.

Length of the tubing is dependent on water temperature you're operating in. I had twin engines of about 250 hp and about 30' of tubing per engine for 55F average sea water temp, but up to 65F when tuna fishing.
New steel boats built at the time used an I beam keel, boxed in as a keel cooler. Usually one side for the main engine and one side for the auxiliaries. In steel coolers, you have to keep fresh anti-rust compounds in the coolant. Otherwise the keel cooler rusts out and is a major job to replace.
Commercially produced keel coolers are more efficient and made out of alloys more resistant to sea water than steel or copper. Although the copper naturally repels marine growth. Because the commercial models are more efficient, they're smaller and produce less drag. When adding them to steel boats, usually an indent is added to the hull so the cooler doesn't stick out beyond the hull plating.
Nice thing about a keel cooler, you don't have the annual cleaning of marine growth from the heat exchangers and don't need a salt water pump.
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Old 02-04-2019, 02:16 PM   #13
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Even if you need to install a larger raw water pump and a larger heat exchanger (seems to be the worst case remedy), I have to believe that's easier and less costly that converting to keel cooling. And you will still need the raw water system for exhaust cooling, even if you move the engine to keel cooler.
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Old 02-04-2019, 02:16 PM   #14
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Have the heat exchangers been professionally cleaned and inspected lately, or ever?
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Old 02-04-2019, 02:36 PM   #15
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Continuous power rating?

Bedford is new to me with this thread so consider this brainstorming.

Are the engines designed to do what you are asking of them? I would expect it to overheat if 80% power is 30% over the continuous rating.

Does the boat have an oil cooler? Oil temp gauge?


This post piggybacks on this question:


Quote:
Originally Posted by Mischief Managed View Post
Are your engines getting to the correct RPM at full throttle? If not, you may be over-propped which would cause the symptoms described.
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Old 02-04-2019, 03:29 PM   #16
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.
Nice thing about a keel cooler, you don't have the annual cleaning of marine growth from the heat exchangers and don't need a salt water pump.
Downside is the rather large added expense of coolant and drag from piping.
Shipwright mate of mine, same engine in 65 fter reckons about $3000 in coolant for his keel cooled vessel vs about $300 for our HE cooled one.
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Old 02-04-2019, 03:34 PM   #17
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Bits of old previously shredded pump impellers can lurk in your raw water system, causing just the kind of havoc you describe.
Most assume that all the rubber from a shredded impeller will be downstream from the pump, but they can also lurk upstream, between the pump and strainer, and will block the pumps intake when water flow is high, ie when the throttle is advanced.
There is normally a bit of backwash when the motor is turned off, that moves the rubbish back towards the strainer, and out of sight.
Drop the pump intake hose at the strainer and back flush it, hope you get a big wad of rubber!
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Old 02-04-2019, 05:11 PM   #18
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Great David!
At this very moment I am changing the gaskets from one of the exhaust manifolds , so, one engine is down.
As soon (perhaps this weekend) I have the boat in working order again I will follow your advise and post it here.

Best regards, Cosme

Can you also get a reading on raw water cooling flow by pulling the hose off of the exhaust injection elbow, put it in a bucket, run it at mid rpms and see how long it takes to fill. Running the engine from cold with no raw water flow to the exhaust won't be a problem. That value plus the in and out temps will tell me a lot about what is going on with your cooling system.


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Old 02-04-2019, 06:04 PM   #19
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Quote:
"When adding them to steel boats, usually an indent is added to the hull so the cooler doesn't stick out beyond the hull plating." End of Quote.

An indent is a good idea if you proceed with the keel coolers, but it's a PITA to clean barnacles and coral worms behind the cooler - almost impossible to get tools in there...
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Old 02-04-2019, 08:59 PM   #20
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I once had a boat with a marginal sized heat exchanger, I went to Sen-Dure here in Ft Lauderdale (they make heat exchangers) and they suggested a second heat exchanger plumbed right in-line with the primary.
Simple, worked

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