Closed Cooling System (Half)

Discussion in 'DIY Marinizing' started by Lawrencemd, Sep 20, 2009.

  1. Lawrencemd
    Joined: May 2008
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    Location: Canada

    Lawrencemd Junior Member

    I would like to get your opinion on the setup of a half closed cooling system for my 250 6cyl boat engine. What I was thinking of implementing is keel pipes cooling the engine and trans oil cooler (closed system) and cooling the marine manifold by pumping in raw water from a thru hull fitting into the marine manifold then out and into the wet exhaust. A seen in the below pic. What size pump do u think I would need for the raw water side (in gph)?

    Attached Files:

  2. mwatts
    Joined: Jul 2009
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    Location: Netherlands

    mwatts Martin

    I always respect guys who attempt to do DIY practical keel cooling... ;)

    A few thoughts:
    • You might have a better chance of a good answer in the "DIY Marinizing" section
    • Where's the thermostat? It will be hard getting the engine at a good operating temperature without a thermostat. As it looks now, it will probably run too cold. Never leave the thermostat out when designing your own cooling system.
    • The thermostat should connect to a valve which will redirect coolant from a continuous flowing loop to the engine, so it starts to get cooled too. You don't want the coolant standing still in the keel pipes, as it could get very cold, putting strain on the engine if it suddenly starts flowing to the engine.
    • You could use a heat exchanger, cooled by the fresh water, as an alternative to the keel pipes.

    Just my $ 0.02. There are bigger experts on this forum with possibly better ideas, but the design you currently have is sub-optimal I think.
  3. thudpucker
    Joined: Jul 2007
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    Location: Al.

    thudpucker Senior Member

    Watts says good things.
    My experience with a 327 Chevvy engine in Cook inlet AK with just the Heat exchanger was great. You dont need a Keel Cooler.
    One more thing you might want to add is a Water Pressure guage to the Engine coolant. It will tell you about trouble before the engine temp guage will.

    You just cannot run any engine without a T-stat. With the Heat exchanger and normal 50/50 Anti-freeze mix you'll have an engine that might outlast you!

    Make sure your sea water pump is accessible for cleaning and have a good strainer on the inlet.
  4. steele m.a.
    Joined: Dec 2007
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    Location: Victoria B.C. Canada

    steele m.a. Designer/Engineer

    I'm building a similar system right now . It's for a 240 ci. mercury straight six .
    Original , the engine pumps raw water up , through itself and it's exhaust system , and then overboard . I live on the West Coast , on Vancouver Island
    and this type of cooling leads to internal corrosion . What I'm doing is modifying the original to have a closed system . In order to do this , some
    things have to change . The best way to cool glycol based fresh water
    is to pump it through a heat exchanger that is bathed in cold seawater .
    Instead of putting an external keel cooler out where it can be damaged ,
    what we're doing is mounting aftermarket automotive transmission coolers
    inside the hull , with open ports bringing raw water in around them .
    The raw water surrounding these radiators enters and exits these dedicated
    radiator housings as a function of forward boat speed .
    The modifications required to the original stock hull involve fiberglassing in
    radiator containment boxes inside the bottom surface of the hull , underneath the floorboards , and creating raw water passages at either end of these cooler boxes to allow raw water to enter and exit as much as possible .
    In Canada's cool waters , this is effective .
    This doesn't solve your exhaust pipe cooling problems though . The effectiveness of a marine raw water exhaust cooling system is that it
    is sacrificial , basically you are simply pouring cold water all over a hot exhaust pipe , and throwing out the result .
    This is very effective , if hard on the exhaust system , but there is almost
    no way around it .
    For the same engine cooling glycol to be used to cool the exhaust header
    sounds like it would work , but doesn't .
    The exhaust header is much hotter than the engine , and boils off your
    system's precious ethylene glycol .
  5. Easy Rider
    Joined: Oct 2009
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    Location: NW Washington State USA

    Easy Rider Senior Member

    As to the question .. I don't know but I can tell you what Jabsco pump I have on my 107 cu in diesel engine. You could call Klassen Engines in the Delta area of lower mainland BC .. I just did and they didn't want to stick their neck out. They just do diesel engines and gas engines produce more heat being less efficient but I think they are almost the same at WOT so I'll guess it would be the about the same as diesel. Since your'e only going to cool the exhaust manifold you probably would be fine w the same pump that I have. I'll try and get the size to you later.


  6. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    What you have invented is the standard solution for all marine engines with a water cooled exhaust, except that you use a keel cooler instead of a heat exchanger and you forgot the expansion tank (you will discover you really need one).

    Any Jabsco or Johnson raw water pump with 3/8" or 1/2" connection will do, but be careful not to exceed the max. rpm. They do not like spinning very fast, most are designed for 2000 or 2500 rpm.
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