how to ? prevent exhaust man. overheating during engine warm-up

Discussion in 'General Maintenance/Repair Questions' started by KEVIN D TOBIN, Aug 7, 2020.

  1. KEVIN D TOBIN

    KEVIN D TOBIN Member

    43
    Jun 12, 2018
    1993 290 sundancer, 7.4L mercruiser repower 2018
    7.4L Bravo ll drive
    I am experimenting with a self engineered closed cooling system, problem is exhaust manifolds not getting enough coolant while thermostat is closed. I am using the old style thermostat housing,but have the screw on tee with the spring loaded check valve removed and plugged, the cap that feeds the exhaust manifolds is over top of the thermostat and does not get any flow until the thermostat opens, so that seems to be it, any thoughts ??? thank you
     
  2. vandal

    vandal Member

    369
    Mar 9, 2009
    Brick NJ
    340 sundancer 2000
    7.4 MPI V Drive
    drill a hole in thermostat in my boat i did 3 to get antifreeze to circulate.
     
  3. KEVIN D TOBIN

    KEVIN D TOBIN Member

    43
    Jun 12, 2018
    1993 290 sundancer, 7.4L mercruiser repower 2018
    7.4L Bravo ll drive
    Well, see the bronze tee, that is not installed, I don't know if I will tee into the the line that feeds the bottom of the manifold or run a new line that will feed a different point on the manifold, but after doing some research I found out that that tee is what that is for, to help cool the exhaust during warm-up when the thermostat is closed IMG_0274.JPG
     
  4. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Your trying to include the exhaust manifolds in the CC loop ? How big is the HE ? I converted my 502 to CC but the manifolds are raw water cooled and my T-stat housing looks completely different from Raw water one.
     
  5. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    To engineer full FWC you need a adequate size HX and engine mounted pump. Exaust manifolds with FWC are plumbed in the bottom and out the top .The top port goes to the top cap of the therm housing.
    waste water from the HX goes into the elbow and out the exaust.
     
  6. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    all types of exaust systems need cooling water flowing to cool the rubber components, this has no bearing on the thermostat. With the T and the therm closed water forces the balls open to cool the exaust, once the therm is open, the balls close and flow goes in the bottom of the manifold up and out the elbow
     
  7. KEVIN D TOBIN

    KEVIN D TOBIN Member

    43
    Jun 12, 2018
    1993 290 sundancer, 7.4L mercruiser repower 2018
    7.4L Bravo ll drive
    sorry it took awhile to get back, Well the HE is 6" dia x 24" long, one of the main problems I am having is I could not fit it where you see them over top of the front or back,this weights too much, I installed where the water heater was, I plumbed it in like I see them, but there is so much heat off those exh. mans., w/out them it would be no problem,but to me it is no sense in having a fwc w/o the exh. mans., I think the problem is not enough flow to the exh. mans.,my new inline coolant pump came today,so I'll let you know
     
  8. KEVIN D TOBIN

    KEVIN D TOBIN Member

    43
    Jun 12, 2018
    1993 290 sundancer, 7.4L mercruiser repower 2018
    7.4L Bravo ll drive
    I'm not an engineer,I'm the guy they come out and see when they can't make something work,Pipe Fitter for 44 years,I build heat exchangers for a living.by the way exaust, is spelled with a "H",nice to meet you thou.
     
  9. KEVIN D TOBIN

    KEVIN D TOBIN Member

    43
    Jun 12, 2018
    1993 290 sundancer, 7.4L mercruiser repower 2018
    7.4L Bravo ll drive
    what I am going to try is to incorporate a bi-pass so that the exhaust mans. are always getting flow, using a inferred temp gauge I can tell just how hot they are
     
  10. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Did 7.4’s ever have the manifolds included in a closed cooling system?

    Maybe you need 2 separate heat exchangers?

    On a side note, I don’t think it’s a good idea to insult someone trying to help you.........
    Pointing out a single misspelling in a post by a knowledgeable and very helpful member when no one here pointed out your grammatical errors is a quick way to cease any future assistance from others.
     
  11. KEVIN D TOBIN

    KEVIN D TOBIN Member

    43
    Jun 12, 2018
    1993 290 sundancer, 7.4L mercruiser repower 2018
    7.4L Bravo ll drive
    well maybe you should practice what you preach, yes most after market offer a full system which includes the exh. mans., when mercruiser made this boat mercruiser did not offer a full system for v-belt 7.4L engine, but crusader did, crusader is just better in every way , monitor does , orca does, to name a few. The dry joint would be a better type exhaust man. for fwc, or for any cooling system for that matter
     
    Last edited: Sep 6, 2020

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