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    #1

    Temp Gauge reading funny

    Since my water pump failure 3 weeks ago, I have been watching my water temp gauge very close. It has always run at the 3/4 mark, between the 175 at the half and 250 at the full position, so I would call it 212 ish.....
    While watching it close, I noticed it is at one spot for a while then climbs up for a while , then back for a while. I am a controls and instrumentation engineer and this does not feel like a gauge or sending unit issue, but that the temp is actually swinging. Has anyone ever played with thermostats ?
    What temp range is standard for the Mercruser ??
    is it a standard Chevy part ??
    can we put in a lower temp thermostat that would reduce the engine temp and help reduce engine oil breakdown ??
    Maybe my thermostat issue ( if I have one ) is letting my engine run hotter and causing my new vaporlock condition ??

    here we go again.....
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    #2
    Sounds like a flaky thermostat. Our boat runs very consistent at 170 deg with a 160 deg thermostat. Heavy loads (2 large tubes) will go up a couple of degrees. Max ambient temps have been low 90's. Our raw water line has - strainer,V-drive cooler,raw water pump,screen,trans cooler,fuel cooler,thermostat.

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      #3
      The only time I've ever seen my temp guage climb is when the impeller needed to be replaced and it was going to overheat. It may be that you're not pumping enough water through your engine.
      Cursed by a fortune cookie: "Your principles mean more to you than any money or success."

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        #4
        I put a new impeller in about 3 weeks ago.... the old one was shedded...
        I think I may take some of it apart tonight and look, exploritory surgery, so to speak.... I was thinking about putting the shop vac on the system, like at the outlet of the raw water pump and suk on the engine a little, maybe with the thermostat cover removed......

        So on the thermostat... is it a Chevy thing or some goofy Merc thing ??

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          #5
          Are You sure you removed all the parts from the shredded impeller?

          Our Merc stays at about 175. If we run for a while and then slow down to idle it will climb, becuase not enough water is being pumped through due to the low RPM.
          Common Sense is not so Common
          Looking for fat chicks for long walks, romance, cheap buffets, and BALLAST.

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            #6
            Originally posted by jciscott View Post
            I put a new impeller in about 3 weeks ago.... the old one was shedded...
            I think I may take some of it apart tonight and look, exploritory surgery, so to speak.... I was thinking about putting the shop vac on the system, like at the outlet of the raw water pump and suk on the engine a little, maybe with the thermostat cover removed......

            So on the thermostat... is it a Chevy thing or some goofy Merc thing ??
            BTW, my temp stays at or below 175. I think it's a goofy Merc thing.
            Cursed by a fortune cookie: "Your principles mean more to you than any money or success."

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              #7
              zad0030 - our Merc 350 Mag MPI stays at a solid 170 deg, unless it's really hot out or a heavy load (2 large tubes/7 people), then it will go to 174 or so. It will stay at 170 deg for 15 min of idling while we use a 12v pump to inflate the tubes. If your temps are climbing at idle you might want to back flush the system and see if anything is stuck in there restricting the flow. When I added a raw strainer I found two pieces of cardboard each about the size of a pack of gum in the V-drive cooler section. Didn't have a problem with temps, but a couple more pieces of debris in there would have clogged it up more.

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                #8
                It seems that 170* - 175* is about the average temp for most everybody's engine. I don't think that a lower temp thermo would be the answer, since the manufacturers designed it to run at 170*. It would be more like a "band-aid" to counter an actual problem.

                A couple of things I would look for: Scored impeller housing, blockage/restriction in the pickup hose or trans cooler, Stuck thermostat or something blocking flow through it, loose belt(s) on raw water circulation pump.
                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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                  #9
                  Also make sure nothing is blocking the water pickup grill on the bottom of the boat. When we had all the rain here, several people had muck stuck in the pickup grille that had been floating in the water.

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                    #10
                    I had a water temp gauge with extreme fluctuation at the beginning of this season. Like a gas gauge when the fuel is low. I knew I needed to replace the circ pump, due to the leakage from the weep hole. I replaced the circ pump and all has been good since.
                    Mike Allen, Tigé owner since 1997

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                      #11
                      Mine runs pretty steady at 175 at normal use.

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