Re: Strange noise coming from motor under acceleration... Mercruiser 3.0 with Alpha O
To me it sounds like it is going to be a noisy rocker or the flaps. A noisy rocker is not always going or be heard. The nut could be just loose enough to make noise at very certain times and speeds they are moving. It is like that certain rattle in a car, over most bumps it is not there, but over the right bumps on the road it is loud any obvious. The valve cover is only held on with a few screws or bolts, it takes 5 minutes to pull it off. But if you don't want to pull it off yet, then as posted before, run the boat, remove the oil cap and put your ear next to the oil fill hole. You will hear it loud and clear. If you do not, then it is not the rockers.
When you say "it sounds like it is coming from here, or there" on boats that does not mean much. Since the engine is mounted under that fiberglass deck, and it is mounted on top of the bilge bay, and there is not sound dampening material like under the hood of a car, the sound is bouncing around that engine area so much it is often VERY hard to tell where it is actually coming from. The sound could be echoing out of the bilge bay and making it sound like it is coming from the rear of the engine, when in fact it could be coming from the oil pan area.
If you think it is the flywheel, then when the sound is getting louder, put your hand on the flywheel cover. A sound that loud, you would feel the vibration. If it is not there, then put your hand on the exhaust riser/elbow and feel that for vibration. Keep feeling different parts of the engine until you feel the vibration. If it is making a noise that is that loud, you are hearing the vibration of sound. That means that you can feel the vibration just as well as you can hear it. unless it is deep in the engine, where in that case I would not be running it until you find it and fix it.
2 more thoughts.
1- you said all that service was done to the boat last Feb. It is very possible that during this service either a bolt/screw was not tightened down or was not used with thread sealer and has came loose with vibration and it is rattling and the sound you are hearing could be the bolt/washer jingling against the flywheel cover or manifold or something else. Go over the engine top to bottom with a wrench and screw driver and make sure all the bolts and screws you can find are snug.
2- you indicated that you used an octane booster. This will not eliminate it being the fuel. You put 87 in your boat, and then added an octane booster. so your fuel is sitting at about 87.5 maybe 88 at best. If an octane booster says it adds 10 points, it is speak in 0.xx points. so 10 points would put your fuel from 87 to 88, not 87 to 97. Most octane boosters in a bottle do not raise the octane more than .5 points. the only way you can try and see if the fuel is not the cause is to drain the fuel, OR run the boat until you have 3/4 - 1/2 tank and then add the highest octane you can find to fill it up. sometimes you can find race fuel at 100 or 103 octane. Add that to your 3/4 - 1/2 tank and it will mix it out to be around 91-92 octane.
I know this might not sound like it is fuel related, or any of the other suggestions made thus far, but you cannot tell us that it is not the problem any more than we can tell you it is the problem until you have examined each suggestion given to ensure it is not the cause of the problem. I have seen way more times one this board than you can count where boaters were sure it was not this or that. After 3 pages of posts, it turned out to be something mentioned back on the first page that was just a blind guess. Until you rule them out 100% by investigating them you can't rule anything out, and you might be chasing a ghost wasting your boating season.
Start with the fuel, you stated before you changed from 91 to 87 and now the problem is here, I don't think that is a coincidence.
To me it sounds like it is going to be a noisy rocker or the flaps. A noisy rocker is not always going or be heard. The nut could be just loose enough to make noise at very certain times and speeds they are moving. It is like that certain rattle in a car, over most bumps it is not there, but over the right bumps on the road it is loud any obvious. The valve cover is only held on with a few screws or bolts, it takes 5 minutes to pull it off. But if you don't want to pull it off yet, then as posted before, run the boat, remove the oil cap and put your ear next to the oil fill hole. You will hear it loud and clear. If you do not, then it is not the rockers.
When you say "it sounds like it is coming from here, or there" on boats that does not mean much. Since the engine is mounted under that fiberglass deck, and it is mounted on top of the bilge bay, and there is not sound dampening material like under the hood of a car, the sound is bouncing around that engine area so much it is often VERY hard to tell where it is actually coming from. The sound could be echoing out of the bilge bay and making it sound like it is coming from the rear of the engine, when in fact it could be coming from the oil pan area.
If you think it is the flywheel, then when the sound is getting louder, put your hand on the flywheel cover. A sound that loud, you would feel the vibration. If it is not there, then put your hand on the exhaust riser/elbow and feel that for vibration. Keep feeling different parts of the engine until you feel the vibration. If it is making a noise that is that loud, you are hearing the vibration of sound. That means that you can feel the vibration just as well as you can hear it. unless it is deep in the engine, where in that case I would not be running it until you find it and fix it.
2 more thoughts.
1- you said all that service was done to the boat last Feb. It is very possible that during this service either a bolt/screw was not tightened down or was not used with thread sealer and has came loose with vibration and it is rattling and the sound you are hearing could be the bolt/washer jingling against the flywheel cover or manifold or something else. Go over the engine top to bottom with a wrench and screw driver and make sure all the bolts and screws you can find are snug.
2- you indicated that you used an octane booster. This will not eliminate it being the fuel. You put 87 in your boat, and then added an octane booster. so your fuel is sitting at about 87.5 maybe 88 at best. If an octane booster says it adds 10 points, it is speak in 0.xx points. so 10 points would put your fuel from 87 to 88, not 87 to 97. Most octane boosters in a bottle do not raise the octane more than .5 points. the only way you can try and see if the fuel is not the cause is to drain the fuel, OR run the boat until you have 3/4 - 1/2 tank and then add the highest octane you can find to fill it up. sometimes you can find race fuel at 100 or 103 octane. Add that to your 3/4 - 1/2 tank and it will mix it out to be around 91-92 octane.
I know this might not sound like it is fuel related, or any of the other suggestions made thus far, but you cannot tell us that it is not the problem any more than we can tell you it is the problem until you have examined each suggestion given to ensure it is not the cause of the problem. I have seen way more times one this board than you can count where boaters were sure it was not this or that. After 3 pages of posts, it turned out to be something mentioned back on the first page that was just a blind guess. Until you rule them out 100% by investigating them you can't rule anything out, and you might be chasing a ghost wasting your boating season.
Start with the fuel, you stated before you changed from 91 to 87 and now the problem is here, I don't think that is a coincidence.
Also, I will check the exhaust shutter but I doubt this might be it, since the clicking sound when they're bad is when idling, not at WOT.
