Water pulling from water pump to exhaust

[Alasdair]

This is a question regarding water from the exhaust. Just launched and I am not getting water out the exhaust. If I disconnect the water outlet from manifold I have water flow when engine running. Does this mean I have a problem with the copper standpipe muffler? Boat is a 1974 Northern 29 with a centrally mounted Atomic 4. Any advice appreciated.

[edwardc]

Welcome to the MMI forum! There's a tremendous wealth of A4 knowledge here, so you've come to the right place.
Someone here will be able to get your exhaust sorted out.

My take on your problem is that its more likely there is an obstruction or collapsed inner lining in one of the hoses, either the feed hose from the manifold to the standpipe, or the exhaust hose from the standpipe to the transom.

For starters, try disconnecting the standpipe end of the hose from the manifold and see if you get water through that.

[Alasdair]

Thanks for the reply. I have attached a picture of my exhaust set up. I was able to manually prime the standpipe by disconnecting water hose from mainfold so I know water can pass through clear hose that runs to top of exhaust. Not sure how the water his drawn up hose and if there could be an internal problem in the 40 year old copper exhaust.

[CalebD]

Standpipe exhaust system

Welcome Alasdair.

Your exhaust system is called a 'stand pipe' exhaust set up. Since my set up uses a water lift muffler I'm not so familiar with the ins and outs of the normal stand pipe set up.

The picture does help (if a little bit on the large size - try to re-size down to 800x600 pixels next time if you can).
What I think I see going on here is the clear hose running from the manifold off to the left in the picture should connect to the hot gas exhaust somewhere at, or after the top of the stand pipe (vertical long pipe section). This usually requires a kind of elbow or "T" shaped pipe to join the wet and gas sections into one output that runs the mixed exhaust to the transom, or wherever your exhaust exits your boat.
For starters though, the clearish hose is likely not really an engine water hose as engine water hose is usually a solid black rubbery affair. The clear hose (if I am not mistaken) is meant for running water lines inside the cabin. If this hose has not melted from the hot water exiting the engine yet it may help you with figuring out what is going on with your exhaust system.

What I would try is to get the engine running with the raw water valve open and peek inside and see if you see any water coming out of that clear hose attached to the manifold. I suspect that it is possible that your engine cooling water is piped over board right there and not joined up with the gas exhaust at all. You'd have to follow that hose and see where it goes to.

Anyway, best of luck.

[Kelly]

Alasdair-

I also have a copper jacketed standpipe after the manifold in my exhaust system. Hot coolant exiting the manifold (or heat exchanger) is directed to the bottom of the standpipe (threaded fixture without a hose at the base of your standpipe?) to help cool the exhaust gases without actually mixing.

The mixing in my case happens after the standpipe so the hot coolant exits the standpipe near the top from a similarly threaded fixture where a hose carries it to the mixing chamber. The mixing chamber in my setup is a separate entity.

Hopefully the following drawing will help sort all this out.

I agree with CalebD that any blockages are most likely to occur in the hoses. Another possibility is a blockage at one of the junctions (impeller vane or build-up).

[Laker]

A key piece of missing information here is : where does the discharge hose coming off the manifold go to? Where and to what does it connect ?

Ditto on the hose type comment ; that semi-clear hose is not the right stuff for that application.

[edwardc]

After seeing your photo, I had another thought.

The top of the standpipe, which is where the water has to be pumped to, is quite high in relation to the top of the engine. It's possible that your raw water pump is working well enough to show water flow from the manifold when the clear hose is disconnected, but lacks enough pressure to pump the water all the way to the top of the standpipe.

It's easy enough to check. Attach a separate hose to the manifold's water outlet, and bring it up as high as the top of the standpipe. See if the engine can still pump water this high. If not, first place to check is the impeller. Make sure all the vanes are present and intact. Also, check the pump's backplate for wear. It only takes a surprisingly small amount of wear there to significantly affect pump pressure.