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Overheating at Idle/No-Wake, fine other times

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    #1

    Overheating at Idle/No-Wake, fine other times

    Had a weekend boating trip half-ruined after my 2002 20i started overheating. It is fine when cruising or at WOT, but at very slow speeds (slightly faster than no-wake, and at no-wake and idle), it overheats. Gauge goes up and I get a warning beep.

    So, in short, if the engine is running faster, it is fine. Running slower, it overheats.

    Everything else gauge-wise seems fine.

    I got under the boat and looked at the intake area, no obvious obstructions. I'll take out the tube that goes from the intake to the pump (is that the Impeller? Front right of the motor, connected to the intake tube?). I'll check the tube for any obstructions.

    If no obstructions, would it be the impeller/water pump is going out? Or does this motor have a thermostat that might be sticking or something?

    Is there anything else to check before removing the pump? Would I REPLACE the pump, or would there possibly be obstructions inside of the pump that could be cleaned out?
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    #2
    Get a look at the impeller. A thermostat or obstruction would most likely still overheat when cruising.

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      #3
      Originally posted by JCP View Post
      Get a look at the impeller. A thermostat or obstruction would most likely still overheat when cruising.
      Ok, thanks... and is the impeller the piece that is connected to the intake tube? The one on the bottom starboard side of the engine, with a pulley on the front that is turned by the main belt?

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        #4
        I found this kit that looks like a rebuild kit
        http://www.go2marine.com/product/775...807151a14.html

        I will confirm that this is the correct one, but is this TYPE of kit what I'd be looking for (again, making sure it will fit).

        Looks like the entire assembly is about $400, so I'd really like to try to rebuild if the impeller is bad...

        Comment

          #5
          That should be the impeller location. I doubt that you will need the body that is shown with that kit. Probably just an impeller and seal.

          Comment

            #6
            Originally posted by JCP View Post
            That should be the impeller location. I doubt that you will need the body that is shown with that kit. Probably just an impeller and seal.
            Awesome! I'm from a car background so I keep thinking "water pump". Similar location in a car.

            I assume replacing the impeller is relatively easy if someone has basic mechanic skills? (I've removed the transmission from a couple cars and replaced the clutch in an import car)

            Thanks so much, you've been very helpful.

            And just to clarify, you are thinking impeller because if it's damaged, then it flows less water.. so at lower RPM when it's moving slower, it's not flowing as much water as needed to cool? And then at higher RPM, even though it's damaged, it is able to flow "enough" water?

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              #7
              Yes, exactly. You should be able to find some previous post that will detail the impeller change if you do a search.

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                #8
                http://www.tigeowners.com/forum/show...ercury-Engine)
                Mike Allen, Tigé owner since 1997

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                  #9
                  If youve got a Merc engine with the composite raw water housing, yes, get the overhaul kit. Those housings are know to get out of round. You also need to back flush the trans cooler if its post impeller and pre engine.
                  Mikes Liquid Audio: Knowledge Experience Customer Service you can trust-KICKER WetSounds ACME props FlyHigh Custom Ballast Clarion LiquidLumens LEDs Roswell Wave Deflector And More

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                    #10
                    Originally posted by chpthril View Post
                    If youve got a Merc engine with the composite raw water housing, yes, get the overhaul kit. Those housings are know to get out of round. You also need to back flush the trans cooler if its post impeller and pre engine.
                    Hmm, I don't know if I have any of those things. It's a 2002 20i with Mercruiser, but the engine was replaced last Spring (by the previous owner). I believe they only replaced the engine and left all the accessories that were "original", though.

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                      #11
                      Take chpthril advice and get the kit. and do the flush. He knows what he is doing.

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                        #12
                        What about the trans cooler/heat exchanger just past the water pump? High speeds may have enough pressure to push water past any obstruction but at idle it may not. Might be plugged with grass or debris, might be worth a look.
                        My life's journey is not ending up looking pretty, its sliding in broadside, used up, worn out, screaming "What a Ride"

                        Comment

                          #13
                          Do you have a flush kit on it? Had a perko flush kit on an old boat and didn't have the top valve capped. Thought it was a bad impeller but checked it and it was good. At speed had enough pressure to pull water all the way thru, but not at idle or no speed. Capping the top valve solved that particular problem.

                          If no flush kit ignore the post.


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