Where does the exhaust actually meet water

[Meauran]

Hello, I'm new to I/O boats and I'm staring at all of the tubing and piping and trying to figure out why there is a coolant reservoir connected to the exhaust manifold.

This is no doubt a silly question to those who know.

Certainly there can't be water on the back side of the exhaust valves in the head, right? That would simply crack the valve when it gets hot and how would you keep water out of the cylinders. The exhaust piping isn't dry, is it? I've read here about a flapper, where is that?

I'm sure there are different types and different cooling and exhaust circuits. I have a 1986 Merc 170/470 so maybe someone could explain that flavor first.

I'm fairly handy around automobiles so I'm trying to apply what I know here.

 

[Haut Medoc]

Re: Where does the exhaust actually meet water

You have a closed cooling system.....
This allows the manifolds to last far longer than if they are raw water cooled...
The maniflod is cooled by the heat exchanger, or else the manifolds would get red hot....
Autos can have air cooled because they are not in a enclosed space......​

 

[Haut Medoc]

Re: Where does the exhaust actually meet water

Hello, I'm new to I/O boats and I'm staring at all of the tubing and piping and trying to figure out why there is a coolant reservoir connected to the exhaust manifold.

This is no doubt a silly question to those who know.

Certainly there can't be water on the back side of the exhaust valves in the head, right? That would simply crack the valve when it gets hot and how would you keep water out of the cylinders. The exhaust piping isn't dry, is it? I've read here about a flapper, where is that?

No, there is a raw water flow to the risers, to cool the bellows & exhaust pipe....
The water shutter is in the exhaust pipe......​

I'm sure there are different types and different cooling and exhaust circuits. I have a 1986 Merc 170/470 so maybe someone could explain that flavor first.

I'm fairly handy around automobiles so I'm trying to apply what I know here.

Good luck with that engine.....

 

[rndcomp]

Re: Where does the exhaust actually meet water

Meauran - I am glad you asked this questions, because I was thinking the same thing. I have the same engine that you do and I was wondering how this all worked as well. It appears that the coolant reservoir flows directly into the exhaust manifold. This makes sense to keep it cool. However, where my confusion comes into play is if the exhaust and coolant are in the same place at the same time, and exhaust leaves the boat, and coolant doesn't, where are they separated? This is obviously a sign that I am not a mechanic, but I would like to know how they work. Only be asking dumb questions can I learn more.

thanks for everyone's patience.

 

[Haut Medoc]

Re: Where does the exhaust actually meet water

They are cast that way with two separate chambers, one for coolant, one for exhaust......​

 

[SuperNova]

Re: Where does the exhaust actually meet water

The coolant "resevoir" (actually it's a heat exchanger) has two chambers and the exhaust manifold has two chambers. Raw water is circulated thru the outside chamber of the heat exchanger and then out thru the manifold and out of the boat. The inner chamber of the exhaust manifold contains the exhaust gasses and the outter chamber contains the water. Think of an automobile exhaust manifold with a coolant jacket formed around it. The water and exhaust meet at the elbow outlet right before it dumps into the big exhaust tube.
--
Stan

 

[Meauran]

Re: Where does the exhaust actually meet water

They are cast that way with two separate chambers, one for coolant, one for exhaust......​

OK, this makes sense then. Thanks.

Good luck with that engine.....​

Yeah, I'm reading that they can be a little "quirky." Of course, you don't need to try to scare me, I'm already having fits over the fact that I overheated mine last weekend. I'm following along on one of rndcomp's threads where he is getting help for the same condition; hoping I haven't ruined anything expensive.

I've got gaskets for all of the front cover accessories coming for this weekend.

 

[Scaaty]

Re: Where does the exhaust actually meet water

A peek inside..

 

[rndcomp]

Re: Where does the exhaust actually meet water

I have n 87 Merc 170 with FWC. I am getting confused with the different names of the the parts. On my engine I have the 'reservoir' (or the place where you actually pour the coolant) right above the exhaust manifold. Next to that (well mounted to the hull) I have the plastic overflow container. Then, below the exhaust manifold I have the long 4" tube which is what I thought was called the heat exchanger (where the sea water cools the fresh water). So what is the riser? Do I have my terminology all screwed up.

 

[Meauran]

Re: Where does the exhaust actually meet water

SuperNova confused me too. My reservoir is definitely not my heat exchanger.

The 'heat exchanger' sits low along the port side of the engine compartment.

The 'reservoir' I'm referring to has a radiator cap on it and is attached directly to the exhaust manifold. I think this is what is sometimes referred to as the 'riser'.

 

[SuperNova]

Re: Where does the exhaust actually meet water

I'll try to straghten it out. The 4" tube along the bottom the the port side of the engine should be the power steering cooler. The plastic overflow bottle is the "resevoir". The big tank looking thing is the heat exchanger. The big cast iron thing bolted to the top of the exhaust manifold, with a 3" outlet hose is the riser and it is where the exhaust gasses and water finally combine.
--
Stan