Where does the water go?

[toolm8kr]

Hi everyone. This is my first post but i have been reading lots on this site and its pretty helpful.

Just a little background on me: I am a mechanical engineer and a toolmaker. I have worked in machine shops rebuilding engines and I have a pretty good understanding of most mechanical systems. I have never worked on a boat though.

I have just bought my first boat. It is a 1979 Imperial, 17' bow rider with a mercruiser 120 I/O. I know that the cooling water is taken in from the lower end, and circulates through the engine to cool it. But where is the water supposed to come out?

When I run my boat on the muffs, some water comes out of a small hole at the bottom of the lower end. But it also comes from the exhaust. Is this normal? I know that my exhaust bellows is leaking so most of the exhaust/water mixture is coming from there. I know that the exhaust is supposed to come out from the propeller but is that also where the engine coolant is supposed to come out too? mixed together?

Please help.

 

[Don S]

Re: Where does the water go?

In a raw water cooled engine, the water comes in thru the outdrive, to the thermostat housing, thru the engine to the exhaust manifold and riser and back out thru the drive thru the exhaust passages.

 

[WizeOne]

Re: Where does the water go?

The cooling water mixes with the exhaust at the back of the risor(s) on the exhaust manifold. It all then goes down the Y pipe and out thru the outdrive and prop hub. Some Mercs have bellows between the transom assy and the outdrive so you see very little water coming out between them. Some Mercs have a tube that attaches to the exhaust port on the transom assembly and does not attach to the outdrive. On those you will probably see more water coming out between the O/D and transom assy.

 

[toolm8kr]

Re: Where does the water go?

thanks for the promt response Don. What about the water coming from the small hole at the bottom of the lower end?

 

[Don S]

Re: Where does the water go?

Look at page 6A-7 of the link below.

http://www.boatfix.com/merc/Servmanl/13/13A6R2.PDF

 

[toolm8kr]

Re: Where does the water go?

That is a great link. Thanks. But it doesn't clear up my question about the little hole in the bottom of the outdrive.

Is the water coming out of there just venting when the impeller is pulling water in, but the thermostat is closed?

 

[Bondo]

Re: Where does the water go?

But it doesn't clear up my question about the little hole in the bottom of the outdrive.

Ayuh,.....

Exactly Which Hole,...?? Exactly Where on the lower unit,..??

 

[BAYLINER185]

Re: Where does the water go?

If you are talking about the two holes on the lower part of the transom sheild they are called the idel releif holes and water should be running out of them when the motor is runnign on "muffs"

Perfectly normal to see water flowing out of those holes + it should feel warm to the touch.

 

[rad1026]

Re: Where does the water go?

I think he is talking about the drain hole at the bottom of the outdrive:

I had a question about that too a while back after I replaced my impeller because I just had never noticed water coming out of that hole when the engine is running on muffs before. I was told that hole is a drain that allows water to drain out of the the outdrive and it is normal to see water streaming out of it when the engine is running on muffs. I hope I understood that correctly.

 

[toolm8kr]

Re: Where does the water go?

Thanks rad. That is exactly what I was referring to.
Thank to everyone for their input. Cheers!