Home Forum Ask A Member 9.9/15 impeller housing tricks?

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  • #12239
    dan-in-tn
    Participant

      US Member

      Just a suggestion for the future if you don’t have a setup for this. Get you one of those goofy looking sockets they show on TV that is suppose to fit any size shape fastener. Next time you have an over heat or water pump issue use it to drive the driveshaft. Get you a piece of copper tubing of the proper size and length to fit the pump grommet. Bend the top of the copper tube away from you (experience). Put the gearcase in the tast tank and run a drill motor. You should get a healthy head of water at the end of the tubing. Keep in mind the drill may not turn the water pump as fast as the motor will idle, but should be close enough to simulate. Just another way to separate different systems on the engine to figure out what your problem is. Be sure and pick the gearcase up high once it primes. Just keep the pickups under the water to see how it reacts.

      Dan in TN

      #12240
      johnyrude200
      Participant

        I pulled the motor completely apart, but not the manifold of course (not necessary…well, actually, now I have pulled the manifold to replace it because the manual starter screw orifice was stripped out and beyond salvage…another whole batch of cursing). The tell tale was gushing water with the garden hose connected to the water inlet tube, and there was lots of water passing through the thermostat orifice. I had to clean out the telltale because the "L" off the water jacket was nearly 100% obstructed with dried up sand/debris. The cylinder water jackets had nothing in them (I pulled the cylinder head…despite this being a salt water motor, only had 1 stuck screw…of course, it snapped and required a drill out and retap).

        When I originally started the motor (first run), water came from the telltale briefly, then turned to a steady drip. There was a very minor amount of water coming from the exhaust of the motor (just below the pan). So there was probably a little water getting through that thermostat bleed hole.

        Upon further education on my own behalf, these 9.9/15hp motors do not have a water bypass as did their predecessors, the 9.5hp’s. So if the thermostat is stuck, that will basically create a ‘damn’ of sorts to the water flow. The telltale will still have water flow but it won’t be able to circulate past the cylinders, because once it passes the thermostat it goes up and around the thermostat cover (which is the outer cylinder head cover), then right out of the motor. Thus, stuck thermostat = overheat condition.

        So once I have the gaskets and replacement thermostat, I’ll be able to button her back up and confirm if this was the issue or not (I feel pretty confident that it is). I had put a new impeller in before I went more invasive and it didn’t solve the problem, which is why I started this thread originally, to see if there were any passages in the impeller housing that I wasn’t aware of that should be examined for clogs.

        Recall a couple of weeks back I ran into the same issue on an older 20hp motor; Frank was kind enough to point out there is a tiny pinhole in that housing which if clogged, essentially shuts off water supply to the motor. That was such a dramatic change (basically like turning a faucet on and off, that’s how much of a difference it made), that I wanted to be sure this wasn’t the same issue. I don’t think the 9.9/15 impeller housings have this type of configuration. If I’m wrong, I hope somebody who’s following this thread tells me for future reference!

        #12241
        johnyrude200
        Participant

          Hi Dan,

          I’ve tried that trick before and it is helpful, the only difference is I didn’t use a copper pipe on the gearcase, but I have leftover parts from other motors I can use to make it a ‘truer’ test. I usually just use a normal battery drill and make sure the teeth on the drill are lined up with the driveshaft splines to avoid mucking those up. It is very helpful…just had to learn to make sure that the gearbox isn’t in gear…because the first time the thing ran away from me and wound up 4 feet down in my oily barrel!!

          Plenty of cussing and a greasy arm fetching that thing from the bottom left me with a good learning lesson!!!!!!

          #12242
          fleetwin
          Participant

            US Member - 2 Years

            A great idea for sure. But, keep in mind that an exhaust leak into the water pump wouldn’t show up with the "drill test". True, it might show up if you pick the gearcase up to expose the water pump once it is primed, but that is kind of a tricky thing to do.
            One thing is for sure though. You have definite pump problems if nothing flows out of a copper tube during this test.

            #12244
            fleetwin
            Participant

              US Member - 2 Years

              Well, I think we are confusing the "bypass" term we are using. The bypass I am referring to is right in the thermostat. In other words, most of the OMC thermostats don’t seal completely when completely closed. There is a little groove in the thermostat cup/housing that allows a bit of water to bypass through the closed thermostat. And yes, there are actual bypasses cast into the block on other OMC engines, but I do not think there is on this 9.9/15. I will have to look at a head, perhaps there is a little bypass/bleed hole in the head, can’t remember. Later model 9.9/15s could bypass the thermostat by pushing the thermostat off its seat (compressing the pressure relief spring above the thermostat), but the early 9.9/15s did not use the pressure relief system, unless someone has replaced/updated the cylinder head.
              You mentioned earlier that there was some sort of gasket under the SS impeller plate when you first looked at the water pump, which makes me question the water pump because no 9.9/15 has used a gasket under the impeller plate that I know of. That is why I recommended replacing the complete water pump, not just the impeller. Don’t forget to check the gearcase/pump plate mating surface, this area is thin and erodes causing an air/exhaust leak into the pump.
              Did you have the cylinder head off when you check the thermostat, or did you just pull off the water cover?
              Does this engine show signs of overheating? Discolored paint, melted wiring?
              I would definitely perform Dan’s drill test, put the gearcase in a bucket of water instead of allowing it to escape into your test tank!
              Will brave the cold cellar, and have a look at a head for a bleed/bypass hole.

              #12248
              dan-in-tn
              Participant

                US Member

                Several more points. First on larger OMC engines the pisser doesn’t indicate anything , but that the engine is pumping water! That may come as a shock since Merc is opposite. I am not positive OMC small engines are that way or that it has always been that way. JohnnyRude those manuals I sent you have a water flow diagram in the rear for each model. Blue is cold water red is hot. Very helpful, take a look.
                The hole that Frank R told you about on the 20hp fills the top driveshaft cavity with water making a seal so exhaust gases are not drawn into the pump. Air pulls into a pump easier than lifting water.
                The copper tube needs to be as long as it is up to the powerhead of the engine, that’s why I said bend it away from you (or you will get an ear full). I figured you would take the prop off since that has nothing to do with pumping water, not like the old days!
                Just put a long bolt in the back of the gearcase to hold on to or bolt you a handle to it.

                Dan in TN

                #12249
                fleetwin
                Participant

                  US Member - 2 Years

                  Another great point Dan. Yes, on most of the smaller OMCs, the overboard indicator is on the exhaust manifold which is at the beginning of the cooling cycle (except for the 4hp models). Sooooo, a plugged thermostat would NOT affect the flow through the pisser/overboard indicator.
                  This brings us back to the pump/grommet/or something before the exhaust manifold. I suppose a blown head gasket, or perhaps an exhaust leak into the manifold cooling passage might affect indicator performance, but that is a longshot and I think you would be seeing water on the plugs.
                  Not trying to minimize things, but it is real common to get crud caught in the indicator elbow.

                  #12257
                  johnyrude200
                  Participant

                    All good info, but again, I need to get the motor back together before I can go further. I am going to run it without the thermostat first (which hopefully will show it running cold), then put a new thermostat in and retest. If all goes well, it should be OK at that point.

                    Dan I looked at the water flow diagram a few times before my initial post and they are very helpful. This is my first batch of 9.9/15’s I’m working on so there is a learning curve going on here, as I’m sure there will be more to come as I move onto other motors once I’m done with this style. Being able to pull the whole motor apart obviously is the best learning lesson.

                    Donny, I am in agreement with you between the two different bypasses; there is a thermostat bypass (on the thermostat, a small vent basically for water), and then some motors have a water bypass altogether (and from what I said before, it appears the 9.9/15’s do not have this). My point before is that the predecessors (9.5’s) had a water bypass, but if the thermostat was faulty the engine would still overheat with a stuck closed thermostat.

                    You’d see water pumping from the water outlet, but the motor would still overheat. It appears with these 9.9/15’s you’ll see the telltale but that doesn’t mean water circulation around the cylinders. It’s sort of a handy feature to help trace the issue – because at least you know water is flowing through the gearcase/water pump. If the stream becomes weak, that tells you ahead of time you have a gearcase originated water pump issue, or perhaps to your point, a grommet that is folded over or a leak somewhere previous to the tell tale.

                    #12260
                    fleetwin
                    Participant

                      US Member - 2 Years

                      OK, yes, that makes sense, guess we were saying the same thing. Unfortunately, it would appear as though a bad thermostat is not the cause of your problem based on your report that there is very little water coming from the telltale. Replacing the thermostat on the early 9.9/15s is a royal pain, I hate to see you doing this job twice.

                      #12271
                      johnyrude200
                      Participant

                        DONNY!!!!!

                        The telltale was clogged up initially, but there was slight water flow. I unclogged it and now water flows freely throughout the motor. I haven’t been able to start it up because I’m waiting for the thermostat gasket and replacement thermostat to arrive this week. Then we can >hopefully< put this one to rest!!!!

                        Will report back 🙂

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