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  1. #1
    Join Date
    Feb 2007
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    Default Heat Exchanger inlet vs outlet temps

    Hi Guys

    Just curious as to what temp reduction percentage one might see on a healthy heat exchanger inlet vs outlet on the closed side at idle and under load.

    Half systems and Full systems.

    Thanks
    Jon Allen

  2. #2
    Join Date
    Mar 2009
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    Portland, Oregon,
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    12,088

    Default Re: Heat Exchanger inlet vs outlet temps

    Jon, I just did a quick search regarding a car/truck radiator cooling percentage...... and found that approx 25% to 30% of the engine's heat is transferred into the engine's coolant. I'd think that those figures would be low given that the Marine Engine is always under load.


    As you know...... the Marine Engine heat exchanger performs the same task as does a car/truck radiator, but with much more efficiency due to the liquid media, versus air.



    .
    Last edited by RicardoMarine; 07-08-2020 at 06:41 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP drives

    "Intellectual growth should commence at birth and cease only at death." Albert Einstein

    Please... no PMs! Post your questions on the forum.

  3. #3
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    Feb 2007
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    275

    Default Re: Heat Exchanger inlet vs outlet temps

    Hi Rick

    Thanks for the quick reply.

    It’s tough to convince a boat owner to allow for a intrusive heat exchanger inspection during a survey.

    I like to see a 40 degree difference at a fast idle and at cruise spd.

    25 to 30 % makes sense.

    Any thoughts on max elbow temp at cruise spd. ?

    I’m thinking 140-160 f

    Thanks Again

    You have been such a big help to me over the years.

    Jon Allen

  4. #4
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
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    12,088

    Default Re: Heat Exchanger inlet vs outlet temps

    ...........
    Quote Originally Posted by jon_allen View Post



    I like to see a 40 degree difference at a fast idle and at cruise spd.
    25 to 30 % makes sense.
    that was an automotive example.... the marine cooling system % may be greater.

    Any thoughts on max elbow temp at cruise spd. ?
    Most will suggest that you should be able to put your hands on them.
    Keep in mind that the elbows only see "spent seawater".
    In other words, they are being fed with the seawater that has already removed the heat from the heat exchanger (half system) or from the heat exchanger and exhaust manifolds (full system).

    I’m thinking 140-160 f

    Thanks Again
    You have been such a big help to me over the years.
    You are very welcome!
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP drives

    "Intellectual growth should commence at birth and cease only at death." Albert Einstein

    Please... no PMs! Post your questions on the forum.

  5. #5
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    8,350

    Default Re: Heat Exchanger inlet vs outlet temps

    I usually worry more about the rise on the raw water side.... 50 deg F rise is a sign of a healthy cooling system on a full FWC Big Block at cruise....60 deg F rise is max I use before its time to start inspecting...some prefer to use a pressure increase to indicate excessive restrictions.

    a 40 deg F delta on the closed side is about the best I've ever seen on a full system....30 deg F is more 'normal' based on my limited data set...and this assumes the raw water side is in good condition.

    As far as the reluctant owner goes, if they don't have a complete log book with detailed maintenance records, they really don't have a basis for objecting....

  6. #6
    Join Date
    Feb 2007
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    Posts
    275

    Default Re: Heat Exchanger inlet vs outlet temps

    Hi Mark

    Thanks for getting back to me.
    Its tough to make a call on a heat exchanger’shealth
    as the flow rate of the exhaust can affect the temps.

    I will take your advice as well as Ricardo’s

    Thank you for all of the great advice you have brought to this forum over the years.

    Jon Allen

  7. #7
    Join Date
    Sep 2008
    Location
    Maryland - USA
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    8,350

    Default Re: Heat Exchanger inlet vs outlet temps

    Agreed that it can be a challenge....on the health side, besides the cooling function, I usually suggest a good visual inspection under the end caps and pressure test....its no guarantee but about the best one can do...

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