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Omc overheating

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  • Omc overheating

    I've read and read forms all day about this and can't come up with the problem. I've posted a few times about other things and mentioned this in another post but the post is dead.
    5.8 omc cobra. I had slight overheat on the lake and now I'm stuck still. Replaced the impeller and the old one looked okay but still but a new one in. If I run the boat on the muffs it's stays cool and water comes out ,warm. If I put the lower unit in a bucket it heats right up and now water exited the outdrive.
    I have flushed water from the raw line back out the outdrive and water exits just fine, I've also took the hoses off he manifolds and fished water through them and water exits fine. I also took the impeller case off and checked for exiting water and it exits. The boat had a new lower half last year and I don't keep the boat in the water and has about 30 hours use. I don't know if that's enough time for the screens to be plugged or not. I'm out of ideas now

  • #2
    So, I took the boat to the local launch and wanted to see what it would do. I launched it and fired it up and all was good. I took it out of the channel for a little test drive and got it up to 28-30 mph and it seemed fine. Temp got to 150. I stoped and took off a few times and it peeked to about 180 tops but once I slowed down in the channel is started working it's way down. Ilthe whole time I was able to pop the engine bay cover off and stick my hands on the manifolds and not get burnt, they were hot but they weren't so hot I couldn't grab them. Should I replace the t stat ?
    I noticed a plug wire bad too so much have a set in order

    Comment


    • #3
      Originally posted by Iboost23 View Post
      If I run the boat on the muffs it's stays cool and water comes out ,warm. If I put the lower unit in a bucket it heats right up and now water exited the outdrive.
      Howdy,

      You cannot run the engine with the drive in a bucket. It will likely overheat and burn up the impeller if you do this.

      Now, if you can get a bucket large enough to get the level of the water up to the same as when the boat is floating in the water, it will work.

      A T-stat will not affect the temperature of the risers. The total raw water flow will however. The T-stat will only control the temp of the block and heads.

      Get an infrared temp device if you want to check your gage. I would say that you have no problem at all.

      Do not try to run the engine with the drive in a bucket.
      1987 FourWinns 211 Liberator, Originally an OMC 460 King Cobra.
      Re-powered in 2006 with a 1997 Mercruiser 7.4L Bravo III

      Comment


      • #4
        Note: you CANNOT run a Cobra drive on land, in a bucket because the impeller will not suck water up from the level of the water intakes, if its not under pressure (muffs) or submerged in the water up to the top of the upper gear housing. Remember the impeller is about 8 inches above the water intakes and rubber impellers suck and move water NOT air! Same is true of a Volvo Penta system or a Merc Bravo system. They all need good muffs that fit tight. A Merc Alpha might be able to prime that way because just like an outboard, the impeller is right above the water intakes.
        A few other points:
        ​The Cobra impeller is very easy to do but make sure that:
        ​the o ring seal for the impeller housing does not leak water when running (I like to leave the cover off after I replace the impeller to check this the first time running it on the muffs after replacement). If it leaks water it can also pull in air when the boat's on plane.
        ​Also there is a little hose hooked up to a little nipple in the impeller housing, this should be open, and if you pull the hose off when its running water should squirt out of the nipple like an outboard tell tale (pisser). This allows the pump to prime easier. If it does not squirt water blow it out with compressed air.
        ​Also, even though the OMC manual says to use OMC gasket sealer on the o-ring seal, it sometimes tries to get out of position even with that. I have found that using a heavy grease like OMC triple guard grease holds the rubber o ring seal in that groove better. I've done many of them this way and they do not leak.

        ​It's a good idea to take the thermostat out and test it with a thermometer, in a pot of hot water. It should open at 160*. These engines should run from 160-175*. The thermostat does not sit in the top of the manifold like on a Chevy small block. It is held into the thermos housing by a rubber ring that you have to pry out.
        1988 Four Winns 200 Horizon
        4.3 OMC Cobra

        98 Jeep Grand Cherokee 4.0 Selectrac
        07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

        "While air doesn't freeze....rust never sleeps"

        Comment


        • #5
          As indicated above, you most likely burned up your new impeller
          1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

          Past Boats
          1970 Wooster Hellion - Merc 9.8
          2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
          1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

          What’s behind you doesn’t matter.Enzo Ferrari

          Comment


          • #6
            Lou c, thank you for all the information , and all the other post ti have replied too. Lots of great information you've left on posts that I have read through. I did leave the cover off and let it run on the muffs and had no leaks. I also pulled the vacuum line off and had a water jet coming out of the nipple.
            I was out about 20 minutes or so tonight and I maybe hit 170-180 and I was doing s lot of stoping and going just to see how it would act. I used bellows adhesive on mine because that's what I read in a post I found, hope that's ok. As for the bucket, thanks for that information everybody. That is something I didn't know or didn't read with all the reading I did today. I am going to take the t-stat out and check it just to be safe.

            Comment


            • #7
              FYI - here is why the bucket doesnt work.

              impeller pumps are not self priming. so to get the water flowing, the pump must be submerged, or located at the water line. the water line on a boat with an outdrive is about 6-10" higher than you can get the bucket unless you put the whole boat in the bucket. once on plane, the forward thrust of the drive in the water forces water up to the impeller, then at that point, the impeller pumps it from there.

              this principle is the same for all manufacturers
              1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

              Past Boats
              1970 Wooster Hellion - Merc 9.8
              2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
              1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

              What’s behind you doesn’t matter.Enzo Ferrari

              Comment


              • #8
                Wanted to bring back up this post. I did a tune up this evening, plugs and wires , which were original from 1990 lol let's just say the boat started and ran better than it ever has since I got it, so July. I had it on the muffs after wards and I I seen it get to 150 which is good , but it hasn't ever got that hot on muffs for me so I looked at the prop and I had no watered coming out of it. So I checked the muffs and all was good and I noticed some water coming out after so I watched it for a few minutes and it would come out and stop. Is that normal or should I have a constant exit of water

                Comment


                • #9
                  You won't always get a lot of water out the prop (like an outboard) the exhaust bellows (if installed) usually has holes in it and most of the water, when running at idle, will drop out under there.
                  1987 FourWinns 211 Liberator, Originally an OMC 460 King Cobra.
                  Re-powered in 2006 with a 1997 Mercruiser 7.4L Bravo III

                  Comment


                  • #10
                    On the Cobra when running at idle you'll get most of the water running out right in front of the front end of the lower unit by the horse shoe shaped anode. When you start the engine you may not see water there for a few seconds but then it should be constant. If you don't see water then try moving the muffs slightly on the lower unit, sometimes you have to move them to get the impeller to prime. I have found that the genuine Merc muffs with the wire retainer that goes thru the water intakes works the best. The rectangular ones don't seem to work as well, it appears to me they making the cups out of harder rubber that does not seal to the lower unit as well....
                    1988 Four Winns 200 Horizon
                    4.3 OMC Cobra

                    98 Jeep Grand Cherokee 4.0 Selectrac
                    07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

                    "While air doesn't freeze....rust never sleeps"

                    Comment


                    • #11
                      Most water is exiting the exhaust bellows bc my are cracked a few more places than normal. The water runs out good and then after a few seconds slows done to stops. I did hold the muffs on tighter by hand and seems to pick the water up, but I can almost feel a surge when I hold them to the lower by hand

                      Comment


                      • #12
                        I wanted to add this. I took the impeller off agin and it looks good. I always ran water through the hoses on the mainifolds and water runs through them out the exhaust bellows. I ran water through the raw line back out the drive and water exits the pick ups and the little pisser. Im highly confused as to why I keep getting warm. The impeller is sealed good and no water leaks when running. Even when I'm holding the muffs tight it's not like it should be.

                        Comment


                        • #13
                          Are you sure that little bleed nipple in the impeller housing that the small rubber hose is hooked up to is open? That helps the impeller to prime. I check this after installing a new impeller, leave the cover at the tail end of the upper gear housing and check for leaks around the gasket of the impeller housing and pull off that hose at the nipple to make sure it sprays water.
                          ​I had this same issue recently and I found that the rubber they are using on the muffs (I used to use the one that has rectangular muffs and feeds to both sides) seem to be made out of harder rubber than the last pair I bought and do not seal that well. I switched to the genuine Merc (Quicksilver) muffs that have the metal rod that goes through the water intakes and clamps together both sides of the muffs and they seem a lot better.
                          1988 Four Winns 200 Horizon
                          4.3 OMC Cobra

                          98 Jeep Grand Cherokee 4.0 Selectrac
                          07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

                          "While air doesn't freeze....rust never sleeps"

                          Comment


                          • #14
                            I can blew through the line when I pull it off. I just fired it back I and I pulled the vacuum line off as the little pissed shot a little water out and after that it stopped and nothing is coming out now

                            Comment


                            • #15
                              Sign up today
                              Lou c , I think it may be the muffs not sealing enough to let it prime. I pulled the impeller off and did the test with the muffs on to see if water sprays out the right side hole and it doesn't unless I use lots of force on the muffs to get it to go up. If I run the hose down the hole it exits easy from the pick up. I'm thinking I just need to get a good pair of muffs or run the boat in the channel and see what it does

                              Comment

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