Idle relief ports

[atistang]

i noticed today while teaching my gf how to drive a boat that while cruising about 10-15mph the exhaust was kinda loud. I stuck my head out and the prop was way under water, but there seemed to be all the exhaust coming out of the idle relief ports.


what speed and rpm is it suppose to switch over? how does it work


1989 3.0 merc alpha 1

 

[Bondo]

Re: Idle relief ports

Ayuh,... There ain't no Switch Over,...

It's Always the path of least Resistance...

 

[atistang]

Re: Idle relief ports

So crusing about 10mph it is normal to get a lot of exhaust from the reilf ports?

 

[JWebber]

Re: Idle relief ports

I would say yes due to the ports being higher in the water line and the prop exhaust being deeper at idle or slow cruise. When up on plane or more engine load the exhaust will flow out all ports and prop. I would check to see if you have of of those exhaust tubes instead of a bellow end to end connection like stock setup or even thru transom exhaust ports.

 

[Don S]

Re: Idle relief ports

Can't say as I have ever looked over the transom at 10 mph and looked and listened to the exhaust relief ports on 3.0L engines and compared the amount that comes out. But if you think their might be to much, pull the outdrive and have a look. A broken exhaust flapper could be partially blocking the exhaust going to the prop.