Merc 7.5 ('75) - lots of work done, motor and water still hot!!!

[metalvolks]

I have a 1975 7.5 Merc 2 stroke. It came with my boat (which has a 115 HP) and i've never used it. Wanted to sell it, so I did some maintenance. Replaced the water pump (impeller and everything that comes with the kit), plugs and bottom end gear oil. I ran it in a trash can for 2 minutes and not much water came of the tale tail and the water was very hot. Exhaust/water jacket cover also was hot.

I took off the power head and exhaust/water jacket cover and it was a mess under there... lots of sand and crap blocking the water path. Dug everything out and took compressed air and made sure nothing was clogged. I replace the 2 gaskets and the powerhead gasket. Also, I replaced the water tube grommet and top piece (plastic piece that the powerhead sits on to seal the water tube).

I started it back up. I have a little better water pressure, but not much and it still gets hot within 2 minutes. What is going on??! What can I do to fix it? I want to sell it and I am in the hole $120 right now (parts) and I don't want to go deeper if I don't have to.

Thank you for any help given.

Paul

 

[green4themoney]

Re: Merc 7.5 ('75) - lots of work done, motor and water still hot!!!

Paul, i have just the video for you my friend... a few tests you can run to see if your water passages are clear.... it sounds like its still not getting enough water......... make sure you have also cleared the water intake to the impeller pump housing.... hope this vid helps

http://www.youtube.com/watch?v=gSWCV2mJz8Q


Ben

 

[metalvolks]

Re: Merc 7.5 ('75) - lots of work done, motor and water still hot!!!

I have done those tests - they pass with flying colors. Water shoots out of the pee hole when connected to a pump and spinning the driveshaft pumps water out of the guide tube.

Another thing that I am noticing is that I get A LOT of exhaust (it's definitely exhaust, blue smoke) coming out of the tail tale. I fear that the exhaust pressure is pushing against the water pressure coming up the copper pipe not allowing the water to circulate. How does exhaust get in the coolant system? I replaced both of the side seals correctly and the powerhead bottom gasket as well as the copper tube grommet and seal. What else could I be missing????!

BTW - I measured compression - 80 PSI on the nose for both cylinders.

Paul

 

[metalvolks]

Re: Merc 7.5 ('75) - lots of work done, motor and water still hot!!!

Forgot to mention, I even cleaned out the water passages behind the cylinder cover (rear of motor) and blew it out with high pressure water. All water passages are clean as a whistle. I'm getting full on exhaust out of the tale tail and sometimes a dribble of water.

Here's the interesting thing.... when I lower the lower unit into a trash can of water, you can hear a "exhalation" of air from the tale tail - don't know if that's a good thing or bad thing. I'm thinking that the pressure of the exhaust is combating the pressure of the water pump and not allowing the water to come up copper tube and cool the motor. How am I getting full on exhaust in the water passages? All new seals by the way...

Any ideas???? I'm about to lose it here!

Paul