Exhaust System

[Bruce Macdonald]

I have a raw water cooled A4 engine, when it is running, I hear a what appears to be a air lock whoose or small bump, like you hit some thing, from exhaust Has anyone experienced this it has just started this year and I have had the boat for some 25 years

[Al Schober]

Bruce,
You neglected to describe your exhaust system. Water Lift? Mixing can?
Also, any visual clues from the overboard discharge - does it do anything different coincident with the 'bump'?
Video with sound would be fun!

[Bruce Macdonald]

Exhaust System

The set up uses a aqualift marine muffler which mixes with exhaust gases in the muffler and discharged overboard through the exhaust port. The noise doesnot happen all the time just occasionly, and not in any sequence, the first time I heard it I thought that I had hit something floating in the water.

[ndutton]

This may be an overly simplistic idea but check that the exhaust hose is securely mounted and not allowed to move about and bang against any structure when the water batches are finding their way through.

After 25 years of ownership I don't need to mention the sploosh sound of the water batches is normal. Darn, I said it anyway.

[Al Schober]

Bruce,
I'm not a waterlift guy, so take this FWIW.
I suspect you've got something going on in the discharge line from the waterlift. Perhaps the inner lining of a piece of hose has delaminated? Certainly worth a check dockside rather than trying to fix what broke while underway. Apparently, 'something' has changed.
In my own case, I have a mixing can with a cold discharge line - hose to rubber muffler to hose to hull fitting. Nothing there to corrode, said I. Turns out the hose to muffler connections were made using short pieces of iron pipe - which corroded and fell apart. Replaced (dockside) with pieces of stainless pipe.

[Bruce Macdonald]

Exhaust system

found the problem, the loop in the exhaust piping was knocking against the hull, have secured the hose and the noise is gone, thanks to all for their help