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  1. #1

    Question Mercruiser 5.7, no flow = overheating

    Hello. This is my first thread so bear with me

    I have a Mercruiser 350 5.7 liters V8 (1990-1995) with a Volvo penta outdrive 270 or 290.
    I have made a full renovation of the engine with new head gaskets, and a lot of new parts.
    After assembly of the engine I have run into a big problem.
    The first test ride ended up stranding me on the ocean because the cooling hose blew.
    After I changed the hose i have noticed that there isn't any flow in the seawater filter. The impeller works fine, as it pumps a good flow of seawater.
    I have learned that there are something called a warm manifold system, and a cold manifold system. I believe I have the cold system.

    https://www.perfprotech.com/blog/art...e-exhaust-tips

    I have the gaskets with the restricted holes between the elbow and exhaust manifold. (worked fine before the renovation).
    I have also tried to run freshwater from a hose through the system, but it won't "take it" through..


    Does anyone have an idea of why the engine overheats and there is no flow of coolingwater?

    Regards Mikael
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
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    Default Re: Mercruiser 5.7, no flow = overheating

    #1. Always run the engine up to temp at the dock after doing work to the cooling system so that you don't end up being towed home.
    Blown hose indicates there was a huge buildup of pressure. You don't specify which hose it was, so we can't really help.
    Practicing the ancient art of ren-ching

  3. #3
    Join Date
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    Default Re: Mercruiser 5.7, no flow = overheating

    Are you SURE you replumbed the cooling properly???? Also check that the holes in the elbows that flow water into the exhaust line is clear... is the oil cooler water path plugged ?
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280

  4. #4

    Default Re: Mercruiser 5.7, no flow = overheating

    Hello. Thanks for the replies.

    I have now tested it again with the hoses to the exhaust manifold taken off.
    There is now a good flow of water through the engine, and the problem is in the Elbow or manifold..

    Do you know if it is possible the clean the Elbows (and how) instead of buying new ones?

    Regards Mikael

  5. #5
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    Default Re: Mercruiser 5.7, no flow = overheating

    The first test ride ended up stranding me on the ocean because the cooling hose blew.

    It blew from the pressure because the water is not leaving the engine thru the exaust.You sure you didnt run thru some mud or sand?

  6. #6
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    Default Re: Mercruiser 5.7, no flow = overheating

    Quote Originally Posted by Mikael96 View Post
    Hello. Thanks for the replies.

    I have now tested it again with the hoses to the exhaust manifold taken off.
    There is now a good flow of water through the engine, and the problem is in the Elbow or manifold..

    Do you know if it is possible the clean the Elbows (and how) instead of buying new ones?

    Regards Mikael
    How old are the elbows and manifolds? Which type?? "Mercruiser Dry Joint" ??? Being plugged and not flowing water is not the worst thing that can go wrong with manifolds or elbows... photo below is a "dry joint" style
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by sandkicker; 05-28-2020 at 08:06 PM.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280

  7. #7

    Default Re: Mercruiser 5.7, no flow = overheating

    Yes. It was deep enough so that would not happen

  8. #8

    Default Re: Mercruiser 5.7, no flow = overheating

    It is a wet-joint.

  9. #9
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    Default Re: Mercruiser 5.7, no flow = overheating

    $ound$ like it'$ time for new. $orry to $ay
    Practicing the ancient art of ren-ching

  10. #10

    Default Re: Mercruiser 5.7, no flow = overheating

    You are probably right.. But I think i will try to clean it 100% to see if it can be saved

  11. #11
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    Default Re: Mercruiser 5.7, no flow = overheating

    Quote Originally Posted by Mikael96 View Post
    You are probably right.. But I think i will try to clean it 100% to see if it can be saved
    You don't clean old crappy exhaust. You replace it, or you will be replacing the engine.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  12. #12
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    Default Re: Mercruiser 5.7, no flow = overheating

    Chris is 200% correct... " Being plugged and not flowing water is not the worst thing that can go wrong with manifolds or elbows... "

    They rust thru and you end up with seawater in the cyinders and crankcase. and if this happens while the engine is running ... :-(

    If these are the original manifolds and elbows, you've done very well. If you engine has "center rise" elbows, I'd look into dry joints (manifolds and elbows) as replacement.
    Last edited by sandkicker; 05-30-2020 at 09:23 AM.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280

  13. #13

    Default Re: Mercruiser 5.7, no flow = overheating

    Yeah okay. The manifold is fine, but the elbows are done..
    Do dry joint elbow fit all types of manifold, or do you need a speciel one?

  14. #14
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    Default Re: Mercruiser 5.7, no flow = overheating

    the dry joint elbows use dry joint manifolds , cant put a dry joint on a standard manifold

  15. #15
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    Default Re: Mercruiser 5.7, no flow = overheating

    Quote Originally Posted by Mikael96 View Post
    Yeah okay. The manifold is fine, but the elbows are done..
    Do dry joint elbow fit all types of manifold, or do you need a speciel one?
    If your elbows are bad, so are your manifolds.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  16. #16
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    Default Re: Mercruiser 5.7, no flow = overheating

    ..... major failure mode of sea water manifolds and elbows is not plugging up but rust thru between the water jacket and the exhaust passages starting from the seawater side of the water jacket. Not inspectable by normal means. In a fair number of cases the first symptom of this is the engine hydrolocking.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280

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