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Fresh water flush

Discussion in 'Cabo Yacht' started by Jrms80, Jan 5, 2016.

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  1. Jrms80

    Jrms80 Member

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    I installed fresh water flush T valves to each motor. After I have the heat exchangers and AC cleaned I plan to flush the engines with salt away after using them as I did with my previous outboard boat. I've read on other forums that some leave the raw water intake valve open when doing this and I wanted to see what you folks here think and if there is a consensus on this procedure. The thought was with it open the hose pressure would keep the salt water out and this way you could never screw up and have no flow.
  2. Capt J

    Capt J Senior Member

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    Are you flushing them with the motor running or not? Be very careful as inboard diesels are a different story compared to outboards and you can easily hydrolock them doing this.
  3. captholli

    captholli Senior Member

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    Please explain your theory of how a diesel engine can be "hydrolocked" if by chance the OP wanted to flush the sea water circuit of an operational motor.
  4. Capt J

    Capt J Senior Member

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    It happens a lot. I also see it on generators on higher speed boats just from running fast without the generator running and seacock open. If you're forcing freshwater through the motor via the raw water circuit (or saltwater without the engine running). When you hook a garden hose to it and are pushing let's say 500 gph at 40 psi through the raw water circuit, and the motor isn't running, it can back flow into the motor, via open exhaust valves, from where the water dumps out the exhaust riser and into the exhaust tube on a lot of boats due to the volume of water and there's no exhaust pushing the water the rest of the way out of the exhaust.
  5. captholli

    captholli Senior Member

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    OK, I'll buy into that hypothesis. What do you recommend to the OP to keep this from happening ?
  6. Bamboo

    Bamboo Senior Member

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    What problem is this fresh water rinse of a salt water/raw water path going to solve?
  7. Marmot

    Marmot Senior Member

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    It's a solution in search of a problem, of course.
  8. captholli

    captholli Senior Member

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    My first thought also upon reading the post.
  9. Capt J

    Capt J Senior Member

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    Shut the seacock, turn the freshwater valve on very slightly to keep the raw water impellor wet, start the motor quickly and instantly open the freshwater valve totally once the engine is running.

    I agree with Bamboo, I've seen very little to gain with freshwater flushing a diesel inboard. Gas inboards it tends to help a lot more because the exhaust manifolds and risers are typically raw water cooled and cast iron and when they go bad they usually destroy the motor. However on a diesel it might extend the already long life of heat exchangers a bit and such.
    Last edited: Jan 5, 2016
  10. Jrms80

    Jrms80 Member

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    Well obviously you guys don't read the BD website.

    You flush the motor with the engine running. This process helps keep salt and other deposits from fouling the raw water circuit orifices which reduces its heat transfer efficiency. Keeping it operating more efficiently until the next time the system is proper disassembled and cleaned is better for the Heath of your motor. The small effiort required to flush the motor regularly is worth it imo.
  11. captholli

    captholli Senior Member

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    I'm lost, please enlighten me as to what I've been missing RE: BD website?
  12. Jrms80

    Jrms80 Member

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    Are you really lost?

    Not sure why there needs to be so much attitude on a sport fish boat owners forum. In any event If you have an opinion lets hear it. If you think it's useless just say so but I'll disagree.

    Over time deposits will form on the heat exchangers, reducing the heat transfer capability/cooling systems efficiency, flushing the motors makes this less likely. The cooling system will be better for it. If you don't want to do it that's fine. Maintain your cooling system per spec and you should be fine. I'm gonna use salt away and fresh water flush mine.
  13. captholli

    captholli Senior Member

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    I apologize for any perceived attitude as none was intended but I have no earthly idea what your referring to when you refer to a BD website? What sport fish owners forum are you referring to? Is that the BD site your talking about? I'm all about learning new things and not closed minded at all. Descaling or boiling out a shell and tube heat exchanger is a good practice and is common but if I read correctly flushing your fresh water or glycol closed loop isn't. I'm lost no tude intended.
    Last edited: Jan 5, 2016
  14. Jrms80

    Jrms80 Member

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    I'm posting under the sport fisher forum on this web site, specifically the CABO owners section of the "Sportfish Yachts" forum. When I scroll to the top of this page that's what is on the header.

    If after reading my posts explaining my rational for fresh water flushing I don't know what else I can add to explain it further. Some here obviously think I'm wasting my time. Fair enough.

    Below us the link to BD if you want to check it out.

    http://boatdiesel.com/Forums/index.cfm?Reset=1
  15. RT46

    RT46 Senior Member

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    JRMS,

    I'm not sure that it is necessary to flush your engines with fresh water routinely.

    There is a giant funnel looking thing (sorry I don't remember the name of it, but its advertised in most boating magazines) that you can attach to yoursea strainer to pour antifreeze (or freshwater) in to flush the raw water side.
    The benefit of this device is that you are not flushing the raw water side under pressure so you will reduce the risk of hydrolocking through an exhaust valve.
  16. Bamboo

    Bamboo Senior Member

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    I'm still not sure what problem you seem to be trying to solve. Are the engines running hot from scale on the raw water side? Is it your contention that a fresh water flush removes that scale? I looked at your link an it was a general search of the site- do you have specific threads which detail the issues you (or others) are dealing with? Please understand there is a great wealth of professionals here of all types- and generally we are quite nice and help each other; many other sites tend to be argumentative. I don't know a single captain on the dock where my boat is that does what you wish to do, nor to I know of fresh water flushing of the raw water path by anyone operating sportfishing boats in other places and I'm personally acquainted with perhaps 100 other working captains..
  17. Capt J

    Capt J Senior Member

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    What he's trying to say is that fresh water flushing the engine helps prevent some scaling of the heat exchangers. But in reality, it might help a tiny bit by maybe extending the cleaning of heat exchangers perhaps an additional year. But on diesels nobody has seen much of any benefit to freshwater flushing them.

    Outboards are a totally different animal because the engines are aluminum and have stainless steel bolts, thermostats etc. So in that case it helps with degredation of the aluminum block, heads, etc. But inboard diesels have very stout cooling systems and the majority of people have seen no benefit or not enough benefit to flushing them.
  18. RT46

    RT46 Senior Member

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    I would not recommend regular flushing of a fresh water cooled modern inboard diesel engine.

    there are some gasoline inboard engines that are raw water cooled that some owners flush with fresh water. The intent is that salt water does not sit in the block.

    BTW, I have an outboard that sees commercial use/abuse 12 months a year. I think I flushed it once or twice to see if the hose connection flush inlet works. The engine has never been winterized and is sitting in the slip in 10 degree weather now. I leave the outboard tilted up. I will be running the boat tomorrow. The engine is 2001 vintage and has unknown hours believed to be in excess of 1000 hours.
    Last edited: Jan 5, 2016
  19. Jrms80

    Jrms80 Member

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    I'm not a professional captain putting thousands of hours a year on a boat's engine. I'm operating a "smallish" diesel sport fisher maybe 150 hours a year. The boats engine components and zincs sit soaking in salt water without operating thousands of more hours a year than someone who uses his boat everyday for work. Sitting mostly unused in that salt water environment is not good for your raw water cooling systems components. "Salt water age" not hours used is a problem. I'm pusseled why this is hard for some here to understand.

    On the chance someone wants to know the answer to my original question this is what I found. Flush with the seacocks open and engine running. With the fresh water hose turned on salt water will not enter the engine even with the sea cocks open. Fresh water is lighter than sea water and will stay in the engine once shut down and any fresh water the engine can't use when operating the flush will push safely out with the sea cock open. This way no chance of a screw up with seacocks. Flush a few minutes, shut down the engine, shut off the water.

    Leave sea cock open or closed whatever you normally do. Your zincs will last much longer and your engines components, while sitting now in fresh water instead of salt will not be as damaged. Finally a small electric heater in the engine room was also recommended to help keep surface corrosion to a minimum, nice idea.

    Solution in search of a problem solved...
  20. Marmot

    Marmot Senior Member

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    If the problem was a need to feel good then you have solved it, otherwise it has just added more parts and actions to fail and cause real problems.

    The scale found on a heat exchanger is minerals precipitated from seawater by elevated temperatures. The tubes get hot in service and scale attaches to them. Running a few gallons of freshwater through the seawater circuit is not going to descale the heat exchangers. Leaving freshwater sit between outings is not going to remove the scale. Zincs are cheap, change them when they need changing rather than kludge some silly flushing system.

    If you really have cooling issues, clean the heat exchangers properly or at least do an annual descale by circulating a cleaning compound through the system. If nothing else it will show you if and how much crud you collect.

    There really should be a sign attached to the structure of a boat visible when approaching the machinery spaces ... "Don't just do something - think about it for a while."