Losing coolant through exhaust

[zigger215]

I have a merc 350 in my 98 hewes craft river runner 210. Recently (last 30 minutes of run time) I've encountered a slight problem

First off, at idle, smoke rises over the stern of my boat and smells like coolant. When I hit the throttle the smoke clears and all is well. Bring it down off step and back to idle, the smoke returns and same with the smell. I'm also losing coolant. I suspect, along with a boat shop in town that my exhaust manifolds are shot. Back pressure is causing coolant to be pulled back through my manifolds and then out the exhaust, I'm confused does this sound right? I'm also going through coolant..I'm new to inboards. Thanks

 

[durban]

Re: Losing coolant through exhaust

iam not an expert on inboards , yes its correct if its coming out exhaust then the manifold is leaking . replace gaskets , i had a similar problem with an outboard motor

 

[tpenfield]

Re: Losing coolant through exhaust

I take it that you have a closed cooling system . . . The exhaust manifolds are a good place to start. It could be as simple as a gasket, but possibly more involved.

 

[zigger215]

Re: Losing coolant through exhaust

It is a closed system. I was told that their could be a pin hole in the manifold. They said there is no way to test for it or no for sure and it was suggested that I just change both manifolds...does this sound a little off to anyone else? I'm very skeptical at this point. I was also told that running the boat more could cause me to drop a valve.

 

[Don S]

Re: Losing coolant through exhaust

It is a closed system. I was told that their could be a pin hole in the manifold.

If the manifolds are also part of the closed cooling system, the gasket between the manifold and riser is the most common place. Never heard of a pin hole in a manifold before, but it is possible, but doubtful that the gasket or a pin hole is the problem. If it were, you would probably end up with a hydrolock of the engine after shutting off and antifreeze getting into a cylinder,.

Most common cause is a leaking heat exchanger. You can remove and drain the cooler, then pressurize the coolant side. Dip it in a tub of water and look for bubbles.

 

[zigger215]

Re: Losing coolant through exhaust

The heat exchanger was my thought exactly. At any rate, this shop is going to be doing the repairs for free (bought the boat two weeks ago) they are replacing both manifolds and all gaskets. Hopefully this solves the problem. I'm just really perplexed, I've heard of bad gaskets causing this problem and I have heard of bad heat exchangers causin it, just never heard of the manifold itself causing this problem