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Yet another overheat investigation-gctid388462

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    Yet another overheat investigation-gctid388462

    Alright, it's my turn for the high rpm overheat mystery--After checking risers and buttoninig back up with proper gaskets, still overheats--new impeller, circ pump, tstat, ran without tstat and still same. I must have an air breach, collapsing hose or blockage----what to check first? The clear hose trick, is it best to run from tstat to manifolds? transom to raw pump? Thanks for any thoughts, I know a lot of yall have been through this lately!

    #2
    Yank off the hose on the raw water pump exit.

    Got good water right after the raw water pump you know it's down stream. If you do not have good water right after the raw water pump you know it's before the pump.

    Post back we can go from there.
    Be good, be happy, for tomorrow is promised to no man !

    1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

    '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

    Manalapan N.J

    Comment


      #3
      MikeMag wrote:
      Alright, it's my turn for the high rpm overheat mystery--After checking risers and buttoninig back up with proper gaskets, still overheats--new impeller, circ pump, tstat, ran without tstat and still same. I must have an air breach, collapsing hose or blockage----what to check first? The clear hose trick, is it best to run from tstat to manifolds? transom to raw pump? Thanks for any thoughts, I know a lot of yall have been through this lately!
      How old are the risers, and do you use them in the salt? How did you "check" the risers?

      Comment


        #4
        MikeMag wrote:
        Alright, it's my turn for the high rpm overheat mystery--After checking risers and buttoninig back up with proper gaskets, still overheats--new impeller, circ pump, tstat, ran without tstat and still same. I must have an air breach, collapsing hose or blockage----what to check first? The clear hose trick, is it best to run from tstat to manifolds? transom to raw pump? Thanks for any thoughts, I know a lot of yall have been through this lately!
        Minor heating at higher RPM that I want to troubleshoot before bigger issue.

        Comment


          #5
          Risers brand new, took them and spacers off and cleaned out before reinstalling. Manifolds less than a year old, and yes, full time salt. Took off tstat to manifold hoses and they produced strong flow.

          Comment


            #6
            MikeMag wrote:
            Risers brand new, took them and spacers off and cleaned out before reinstalling. Manifolds less than a year old, and yes, full time salt. Took off tstat to manifold hoses and they produced strong flow.
            Gotcha. Just wanted to make sure they weren't old risers that looked good from the OUTSIDE

            Well, you already know this but it sounds like a flow restriction... if you have closed cooling I'd check out the PS cooler and heat exchanger for blockages as well as the circulating pump (NOT the drive water pump).

            Comment


              #7
              I am having the same sort of problems with my boat. Exhaust elbows running 190 degrees at idle. Steam coming out through prop.Good flow out of the seawater pump, thermostat working fine, manifolds, risers and exhaust elbows almost new. Heat exchangers recently checked and almost new. When I took off the exhaust elbows off I noticed the water flappers on the one side are missing. After talking with my mechanic he tells me this is not uncommon and the flappers are probably stuck in the leg somewhere near the prop and restricting the flow. So needless to say I will be hauling my boat this weekend and removing the lower section of my outdrive and trying to find pieces of my water flappers. Will let you know if this is indeed my overheat problem. I sure hope so because I'm running out of things to check.

              Comment


                #8
                The flappers check is on my list as well, they surely haven't been touched in 12 years!

                Comment


                  #9
                  Found some intersting stuff today---hooked a clear hose up between thermo and Stbd Manifold, witnessed a large air gap that would not fill in at idle, turbulent bubbling water at rev at the dock! Dropped the raw water pump, impeller still looking good--But---when taking off raw water transom pickup line (boat is on water) noticed a pretty weak stream coming out of hose. I seem to remember a strong current coming out that I would quickly have to plug while changing impeller. So I'm thinking a blockage or kink between pickup and pump. Any ideas on cleaning out while the boat is in the water? Backflush, compressed air, etc? Hate to haul out the boat again as I don't own a trailer. I can even put on a tank and take a look from the outside as well, but not really sure if any blockage would be visible without dropping the drive?

                  Comment


                    #10
                    You could use compressed regulated air to shoot backwards towards the drive maybe you picked up some seaweed or maybe mussels living in your drive.

                    I always start from the water pickup and work my way forward for a blockage. See that thru hull fitting in the transom that brings the raw water into the engine on the outside of the hull is where i find alot of blockages.
                    Be good, be happy, for tomorrow is promised to no man !

                    1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

                    '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

                    Manalapan N.J

                    Comment


                      #11
                      Thanks Chief, will try to backflush---Is there anything I can check for while the boat is still in the water? I don;t know how feasible it would be to yank the hose off the transom nipple while boat is in the water, but I could have a blocked hose ready to switch it out and inspect the raw pickup for blocks/kinks too.

                      Comment


                        #12
                        Chief Alen wrote:
                        .............. or maybe mussels living in your drive.
                        Don't laugh at that one!

                        I can tell you first hand that these little suckers will find their way into small cavities, and will grow to the point of restricting water flow.

                        Then they die off, but the shells remain.

                        If all else proves to be OK, this is certainly worth checking.

                        .
                        Rick E. Gresham, Oregon
                        2850 Bounty Sedan Flybridge model
                        Twin 280 HP 5.7's w/ Closed Cooling
                        Volvo Penta DuoProp Drives
                        Kohler 4 CZ Gen Set

                        Comment


                          #13
                          One other question for the experts--I have the raw water pump in hand, I notice there is a small amount of freeplay in the pulley shaft, maybe an 1/8 rotation before it engages the pump--normal? I'm looking at every little thing here!!

                          Comment


                            #14
                            Mike, look at the two thrust surfaces within the pump body.

                            If these aren't in near pristine condition, it will cause pump issues.

                            Our Big Chief Doug C. had this issue.

                            He ended up doing a conversion from his belt driven sea water pump, to the Johnson crankshaft sea water pump.

                            If that's an option for you, it may be worth considering.

                            .
                            Rick E. Gresham, Oregon
                            2850 Bounty Sedan Flybridge model
                            Twin 280 HP 5.7's w/ Closed Cooling
                            Volvo Penta DuoProp Drives
                            Kohler 4 CZ Gen Set

                            Comment


                              #15
                              Now that is a nice option, considering the hassle of changing out the bravo pump (although I'm unfortunately getting pretty quick at it!) I don't think this bit of freeplay would point to high rpm slipping issues, but was just wondering if others have a bit of play or is it 1:1 pulley to pump rotation...! Will pull it apart to insepct....

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