1983 150HP Merc V-6, Weird noise, plz help

Just bought this boat, and this site was really helpful last week. I think it's running too hot, and inconsistent water at tell-tale. I replaced both T-stats and water pump rebuild kit Friday night. It's running equal or less water from tell-tale now. It can't be right, after running a couple miles on plane and coming straight back to idle, there's just drips of water coming out. I'm going out now to remove all hoses and check for blockage, maybe even lower unit, and T-stats to try and force water up the line, and out top of motor. Pressure guage never gets above 3-4 psi? Is pressure samples at top of motor, or down by water pump? I see a pnumatic line down there?

Also, while on plane, there is an intermittent "screeching" noise (also present last time out with old parts). You can throttle up or down a little bit and it goes away then comes back. Almost sounds like a high frequency vibration or something. Very anoying. I'm hoping one of you guys knows what this could be. Sorry for limited info.

Re: 1983 150HP Merc V-6, Weird noise, plz help

Does the screech come from control box (throttle).Sounds like it might be a sick overheat or oil warning horn.Does the water shoot out when up on plane?If you have issues with cooling system/overheating,DO NOT RUN MOTOR.or it will become an ornament,something to rest your beer on,while you row out to sea.

Re: 1983 150HP Merc V-6, Weird noise, plz help

Thanks for the reply. Yes, it's flowing a weak but decent stream when up on plane. It just should be more, especially when I come back off plane, motor is warm, and right to an idle. It just seems weak, and I think it's running too hot. Haven't ran much, need to get this figured out. Water pump rebuild kit I got did not contain a rubber seal that I see in the parts diagram. Wasn't there when I tore it down either. It's the seal that goes inside the sleave (where the copper water tube mates into the plastic sleave at the top of the assembly). I think maybe most of my water pressure is leaking here into the mid and never making it to the motor??? Any thoughts? Also, I cannot find any type of overheat or temp sender anywhere????? Is this connected to the horn for overheat alarm? Water out the pee hole is pretty warm, maybe 110 to 120 I guess.

To answer your question, the noise is coming directly from the motor, not control. Like a weird high freq. vibration or something. Comes and goes. Getting good cooling water should be a fundamental prob. it's kicking my *****... Removed all hoses, and there is no blockage I can find.

Re: 1983 150HP Merc V-6, Weird noise, plz help

Positive displacement (paddle) pump and a high pressure cooling system. The missing seal is critical. If you haven't done major damage by now, you should buy a lottery ticket.

Re: 1983 150HP Merc V-6, Weird noise, plz help

Has your motor been used in salt water?If so you could have some serious build up around the head,it gets as hard as rock when allowed to build..Get a good mech to check it out.your problem sounds critical to the future of your motor.

Re: 1983 150HP Merc V-6, Weird noise, plz help

Fiberglass bass boat, no signs it's been in salt water. I ordered the seal from Crowley 2-day air. I assume it simply mates up with the copper water tube (inside the sleave) when re-installing the lower unit. I didn't run this thing over 25-28 miles per hour for more than 3-4 minutes at a time. It is sending a decent stream when on plane. My hope is that it hasn't gotten hot enough to cause any damage. Thanks for your help and continued comments!!!

Re: 1983 150HP Merc V-6, Weird noise, plz help

The seal just fits down inside the tube projecting upward from the pump body. I wonder if the old one is in there, just looks like part of the plastic. I can't imagine getting much pressure without it.

If it's so crudded up you can't identify it, it probably needs replacing anyway.

Install is easy. just lightly grease it, inside and out, and stuff it down in the tube. There should be a thin plastic guide tube that slides in on top of it and extends a few inches upward. That's just to make it easy to get the water tube in the seal. With a touch of grease, the tube slips in easily.

Re: 1983 150HP Merc V-6, Weird noise, plz help

j_Martin - Thanks for the reply! There was NOT a rubber seal inside the plastic guide sleave when I pulled the other unit out. And there was not a rubber seal included in the water pump rebuild kit I bought at the local boat shop. The upper gasket was also missing from the rebuild kit. The motor was apparently running without this seal installed before I bought it two weeks ago. I tore into it because the water flow just didn't seem right. Thanks to you folks I am learning the error of my ways....

Re: 1983 150HP Merc V-6, Weird noise, plz help

The seal is not normally included with the gasket kit. It doesn't fit inside the plastic tube, but below it in the pump exit tube. The plastic sleeve has nothing to do with actual function, just a guide for assembly.