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1999 75HP Force - Blown Powerhead Gasket?

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  • 1999 75HP Force - Blown Powerhead Gasket?

    What are the symptoms of a blown powerhead gasket on these motors?

    I got the boat about 4 months ago. The guy that had it before me only had it for a couple of months (I've got the paperwork where he bought it) and due to health issues (older gentleman) could not climb up and down the decks easily and wanted a pontoon instead. The guy before him had repowered with a 1999 Force 75HP.

    The guy I got it from said it had a "miss" to the engine and thought it was trash in a carb or something. I got a good deal and turned him onto a pontoon.

    Boat ran fine except it did have a little skip. I changed the plugs (replaced with what was already in it) and changed the primer and quick connect on the fuel line. The engine perked up and we ran it several times all day with no problems. Compression test showed 148psi on all 3 cylinders and all 3 are firing.

    One day I ran it about 30 minutes out and stopped to fish. It would not restart. Spin the engine over for a couple of minutes (that's a looooong time) and it would finally start and run like crap for 10-20 minutes and finally clear up and run like nothing was wrong.

    Discovered the fuel filter was empty when this was happening. Replaced the primer again (could hear gas flow back to tank when bulb was turned on it's end) and also found a bad diaphragm and gasket in the fuel pump. Rebuilt the fuel pump.

    Ran the boat another trip and same old story, run for a while, stop and fish and it would not restart.

    Fuel filter was again empty. Removed quick connect from engine, spin engine over for a minute to dump any fuel inside the carbs or cylinders and reconnected fuel line and it restarted after being primed. I did this several times and each time this would "fix" the problem or at least get me back to the ramp.

    I knew I had some downtime, so I dropped it off at a marina. He replaced the thermostat, plugs and quick connect on the tank. He said the QC was wrong (it was) and the plugs were not the correct plugs for the motor. He also said the motor was running hot (this had NEVER been an issue) and water tested.

    I put it on the water that day (Sept 15) and it ran great until about 6pm. I had to use the trolling motor to get back to the ramp. The boat finally started back up and ran fine.

    Took the boat out Sunday Sept 18 and it ran fine. I fished off and on until after lunch and it would not start. I pulled the QC, spun the motor and reconnected and it started. It ran fine for a minute or two and the overheat alarm went off. I shut it down. After sitting for about 30 minutes I restarted and it ran fine.

    Rode for about 15 minutes and the alarm went off again for a few seconds (long enough for me to turn around to look at the pee stream) and the alarm stopped. Ran another 10 minutes or so and overheated again. Shut it down. Trolled for a few hours and got ready to leave and nostart. Remove QC, pin motor, reconnect, jump on top of the water and hit the ramp with no more problems.

    Had the boat sitting in the marina driveway in Alabama when they opened on Monday morning. I had to leave it and get back to Atl for a meeting.

    Talked to the owner later that afternoon and he said the carbs already had new kits in them and everything was properly adjusted. Checked the floats and the needle & seats, everything looked fine. Then he noticed the powerhead gasket was blown "and should have picked up on that the last time it was there because it was a very common problem." He said that it looked like it had been leaking for a long time and he could see where water was coming out of it and some of the bolts in the area were rusted.


    I've never worked on 2 stroke engines but was a dealer tech for many years on everything from cars to heavy equipment. I know how to fix a 4 stroke engine and how they work, but know very little about 2 strokes.

    I've got a bad, bad feeling about this. Part of me think I'm paying for crap that is not broke (I tested the thermostat that he took out 50 times and it never stuck with me).

    From my limited research, it looks like the powerhead gasket is the gasket on the bottom of the powerhead. What is this thing sealing up? Could it cause an overheating condition or the conditions that I have described?

    Usually I don't let others work on my own vehicles, but we have been busy with work and my mother had a heart attack and triple bypass during all of this. Between trying to take care of her and catching up work I have not had time to do much with this boat.

    I just have a bad feeling about it. I plan on heading over tomorrow and having a come to Jesus about it. I just want to know what I'm talking about before I get there.

    PS. I always mix my oil and gas at 50:1 and add green Stabil and an ounce of Seafoam per gallon of gas. I have no clue what was used it in before I got it.

    It just runs to darn good when it's running good for there to be anything major wrong with it.

  • #2
    Re: 1999 75HP Force - Blown Powerhead Gasket?

    Spotco2 I am much like you in that I was a Auto Tech for years and have been around boats sporadically for years but never wrenched on them professionally. As long as you learn the fundamentals and understand them thoroughly then you can ease some fears and save some frustration and make better choices as well.It should be noted that a head gasket problem on a outboard motor is not the same as it is on a 4 cycle car motor it is a common practice to R&R the heads on a outboard just to remove carbon and inspect the health of the motor.Of coarse as with a 4 cycle motor the cause of the failure needs to be determined as the repairs are being performed or the replacement gasket will also fail.Similar procedures between head gasket replacement are to insure the flatness of the mating surfaces and machine them flat if need be and replace faulty fasteners and to apply proper sealer to the good fasteners and torque down using recommended values and sequence.Also some motors require a re-torque after being ran for a certain amount of time.I'd say go ahead and repair the head gasket it may not be your only issue but at least you'r repairing a known issue.2 cycle motors rely more on sealing of components even more so than 4 cycle motors due to using the crankcase as a functioning pressure vessel for induction of the fuel air oil mixture.I am just learning to wrench on outboards so please read and use what I say knowing that I am not a Marine Outboard Guru I know there are lots of threads and people here that can and will help you so just keep reading and you will learn what you need to know.Sounds like you have more than one problem here. Air in the fuel line in a 2 cycle is a very bad thing because when running lean the engine produces more heat and at the same time isn't getting enough lubrication due to the oil being in the fuel.This could cause your overheating issue and could lead to the head gasket failing.Id recommend a thorough inspection of the fuel system from the tank vent all the way to the induction point inside the crankcase first.Primer bulbs should get firm when squeezed because they just prime the pump and push against the rubber diaphragm inside they should remain firm after pumping them if not there is a air-fuel leak somewhere.Check all quick connect o-rings for signs of wear and replace if needed.Check tank outlet check valves fuel should not return to tank when engine is stopped.Primer Bulb also has inlet and outlet check valves check for proper orientation of primer bulb I.E. look for flow arrow on bulb.Also post back what you end up finding or what fixes your problem after you get it fixed so we can learn from you.You need to find and fix this fuel issue because it is the root cause of the overheating issue IMHO Good luck


    • #3
      Re: 1999 75HP Force - Blown Powerhead Gasket?

      There are no check valves that stop fuel from returning to the tank other than the squeezie.
      The I/O's have a anti-siphon valve in them at the tank.
      The outboard pumps aren't strong enough to suck past the valve.That's why they have a squeezie.New squeezies can be bad right out of the box(Tempo's seem to be the worst)
      The bulb should pump up hard and then after starting it should soften some but not go flat.
      Check the tank vent for blockage or twists in the line.

      The head gasket:if there is no water on the plugs or in the cylinder and the comp is good.It's probably good.
      If it leakes between the cylinders the comp would be low between the affected cylinders.
      What are the comp readings??
      Any inline connectors? The Ethanol in the gas destroys the seal and it can suck air.
      First post in this section.There is a linc by FrankA called a linc and sinc.Do that it might help.
      Carbs reset the air screws 1 and 1/16 turn out.Final setting in the water.
      The enricher could be bad(ethanol again).

      Tallwill38 Appreciate your trying to help. Take a breath and seperate you statements, it's almost impossible to read a post like that.

      Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
      ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

      In Scenic , Beautiful San Sebastian by the sea Florida

      88 Bayliner 21CC 2001 Mercury 225 HP EFI


      • #4
        Re: 1999 75HP Force - Blown Powerhead Gasket?

        Thanks guys for the info.

        This is not the head gasket though, but the gasket under the entire powerhead between it and the exhaust plate.

        I can understand why this would cause an overheat condition because he said that water was coming out. I just can not get it through my thick skull why this would cause a fuel delivery issue and more so why it never ran hot before he started working on it.

        I really want to trust my mechanic (I know a lot of people that use him and have never heard any complaints), but I've been a mechanic for many years and know a lot of them very well.

        It just feels like he is fixing things that are not part of the problem that I brought it to him for.

        Sort of like if I had a customer bring me a car that was running rough and I found their brakes were worn out. Sure I'd try to sell the brake job, but I would also fix what the car was brought in for originally.


        • #5
          Re: 1999 75HP Force - Blown Powerhead Gasket?

          LOL yeah sorry bout not spacing that out is kinda hard to read will definitely work on that.


          • #6
            Re: 1999 75HP Force - Blown Powerhead Gasket?

            The base gasket does not seal any water passages. It primarily seals the exhaust into the downtube. However, the base gasket does seal where the water enters the block through the match plate. Again, however, unless the gasket has failed completely, it will not starve the engine for cooling water. You may rightfully ask: If it doesn't seal water, why does it leak? The spent cooling water is dumped into the leg at the back of the block right behind the bottom of the head. It mixes with exhaust and will be blown out a failed gasket. BTW: I have never seen a base gasket fail at the water seal where it enters the block.

            You mechanic said the engine was running hot, but did he replace the water pump impeller? It is the most likely suspect in cooling problems and it is possible that it wore during the time you brought the engine to service. Possible, but not probable.

            Remove the fuel fittings from the hoses and check them for partial clogs, Clean them well. Check the fuel lines for deterioration and replace if necessary. Your engine should have had Mercury fuel fittings, however, no fitting is "wrong" unless it is too small to pass the required fuel. Chrysler or Force quick-connects are acceptable.

            Plugs should be Mercury (Champion) L 76 V. You can however use Champion L 20 V, NGK BUHX or BUHW, or the Autolite equivalent --I forget the number, something like 2684.

            Have you ever heard the maxim: Trust everyone but lock all your doors? I'm not saying you are being taken, but before you let any more work be done, run the engine and check for a leaking gasket. It will usually fail on the side and squirt water into the cowl.


            • #7
              Re: 1999 75HP Force - Blown Powerhead Gasket?

              Originally posted by Frank Acampora View Post
              You mechanic said the engine was running hot, but did he replace the water pump impeller? It is the most likely suspect in cooling problems and it is possible that it wore during the time you brought the engine to service. Possible, but not probable.
              No he did NOT even check the impeller or even mention it and that is one of the things that irk's me. I'll probably pull it once it gets home.

              I've ran that boat long and hard since I got it and it never ran hot until he got it. The only thing that I can think of is the plugs that I replaced were lower in the heat range than what was supposed to be there. When he replaced them with the correct plugs it heated the engine up. I tested the thermostat that he replaced literally 50 times in a controlled enviroment and it never failed to open or close.

              That don't really matter much because it has already been replaced and paid for. It does make me question him though.

              I appreciate the info about the gasket and plate. If the gasket is leaking, then it needs to be repaired but I must get the fuel problem resolved before I can even sell the boat or motor.

              I'm sorry for the long post, but I guess I just needed someone to vent to about this.


              • #8
                Re: 1999 75HP Force - Blown Powerhead Gasket?

                He could have ran it without water.Or not enough water.J

                Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
                ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

                In Scenic , Beautiful San Sebastian by the sea Florida

                88 Bayliner 21CC 2001 Mercury 225 HP EFI


                • #9
                  Re: 1999 75HP Force - Blown Powerhead Gasket?

                  Could also be the fact that its a bad economy for all and (maybe?) He is trying to pinch a few extra bucks. Who knows. One thing though is check your exhaust plate for any loose or missing bolts, the ones on the bottom can work out and fall in the lower cowl. Loose bolts will cause a water leak right at the bolt holes. Im not saying your mech. is a bad person, just that even he may need the extra $. Change that impeller as already stated. That should be the very first thing to do when we have cooling problems.


                  • #10
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                    Re: 1999 75HP Force - Blown Powerhead Gasket?

                    I don't know.

                    He's covered up with boats and has more work than he can get finished in a reasonable time.

                    There's no telling really. I am going to try to get over there tomorrow morning unless something comes up.