exhaust route question on volvo penta dp-sm outdrive

[striper007]

First time taking my boat out last weekend and noticed while underway about 30 mph the exhaust was only comming out of the exhaust port relief area under the transom assembly. I decided to stop and take a look because this did not seem right.i decided to accelerate in neutral to see what happens. Again only bubbling out from bottom of transom.isnt the exhaust suppose to exit through the rectangular cavitation port too? Any info is appreciated.

 

[ozvader]

Re: exhaust route question on volvo penta dp-sm outdrive

At idle most will come out at the relief port but at speed you are correct it should be out of the cavitation plate. Can you get your boat out of the water to test it with muffs on. Might need new bellows or maybe they are loose if you are lucky.

 

[striper007]

Re: exhaust route question on volvo penta dp-sm outdrive

At idle most will come out at the relief port but at speed you are correct it should be out of the cavitation plate. Can you get your boat out of the water to test it with muffs on. Might need new bellows or maybe they are loose if you are lucky.

Tried that already. Everything is new and tite.i plugged the exhaust relief port with a piece of wood for the hell of itjust to see what happens. The exhaust then came out the cavitation port. So no restriction there.bellows are new and tight so im not sure whats goin on.im thing of making a small plate that will cover the exhaust relief port and maybe drill a 1/2 whole in it for water to drain out.i believe this mite be a bad volvo penta design.maybe to much head water pressure on the rec cavitation port area so the exhaust is dumping out the exhaust relief port instead the path of least resistance.

 

[David Ferguson]

Re: exhaust route question on volvo penta dp-sm outdrive

I started noticing that myself last season. When idled at the dock, the exhaust bubbled up against the transom. Either that is something new, or I never paid attention before. When I checked it out at drydock, most water comes out there also, with only some from the cavitation plate. I never even knew it was considered a 'relief port'.

 

[striper007]

Re: exhaust route question on volvo penta dp-sm outdrive

I started noticing that myself last season. When idled at the dock, the exhaust bubbled up against the transom. Either that is something new, or I never paid attention before. When I checked it out at drydock, most water comes out there also, with only some from the cavitation plate. I never even knew it was considered a 'relief port'.

Yea im thinking volvo didnt engineer this to well. If you can when your in the water next time put the boat in neutral and rev the the engine a bit while the outdrive is down and see if the exhaust exits the rear cavitation port. Thanks.

 

[Don S]

Re: exhaust route question on volvo penta dp-sm outdrive

There is nothing wrong with the design. Those ports are called idle relief ports, and all manufacturers of outdrives use them. Yes, you will see some exhaust out of those ports at speed, but most of the exhaust will be going out through the prop on a DP drive and not be visible in the prop wash.