Mercruiser Exhaust Water Shutter

[pmergler]

When I did my end of year service last winter I split my lower unit and saw the pieces of my exhaust water flapper/ shutter in the bottom of the thru prop exhaust chamber.

In doing some research here and with fello boaters it looks like the repair is pretty straight forward, I just need to order new exhaust water shutters. I came across 2 different products by Quicksilver (http://www.go2marine.com/product.do?no=92309F) and Sierra (http://www.go2marine.com/product.do?no=159228F) as these are the A3 that replaced the old style A2s. There is a significant price difference between the 2 at $70.49 for the quicksilver and $30.97 for the Sierra. Anyone have any input into which part is a better part?

In the product pix the Sierra part looks like when the shutter is closed it is completely closed, in the pix of the Quicksilver it looks like there is are a couple holes in the shutter around the hinge, but it is tough to judge from a product pix. I would think you wouldn't want a part that can allow water through when closed....defeats the purpose correct? But maybe the shutter is sufficient and the holes allow for less back pressure? Just thinking out loud here....

thoughts?

 

[Chris1956]

Re: Mercruiser Exhaust Water Shutter

That happened to me several years ago. I went to the Mercuriser dealer to get replacements and he told me I did not need them. Since he had a vested interest in selling them to me, I took his word for it and left them out. I never had any trouble.

 

[ziggy]

Re: Mercruiser Exhaust Water Shutter

hard to say what the difference is. only thing for sure is that the serria is a copy of the oem. so did they use the same materials for making it? i've no idea. i usually like oem because it works the first time i put the part on. flappers, may not be so precise of a thing. so maybe the cheaper seirra is ok. if you don't let your engine overheat. either or will probably do. if you overheat, either or will melt off too. maybe cheaper is the way to go.
as for the holes in the oem one, by the hinge. if it's oem. it must be the way they want it. flappers i think are designed to slow, not stop, the inrush of water flowing up the exhaust pipe while backing, having a following sea, or a quick close of the throttle, or while beached with waves beating you into the beach.
myself. i like the possible piece of mind they give me when in place. water rushing back into the exhaust sounds like it could be engine killer. with that said, i hear volvo don't run flappers on some of their engines. i hear many folks that just leave them out like chris.... myself. i'd prefer they be there, oem or aftermarket???? i don't know. but i'd put them back, if it were me..

 

[haulnazz15]

Re: Mercruiser Exhaust Water Shutter

Upon rebuilding the transom on my I/O, I went ahead and replaced all of the gaskets and such. I also had heard about the exhaust flappers and decided to look at mine (1976 boat mind you), there was nothing there except the metal hinge on both sides, lol. Rotted or melted rubber lined the metal rib. I am also running an exhaust tube instead of the OEM ehaust bellows, which supposedly protects the exhaust y-pipe even less from oncoming tides.

Now I don't know how long the flappers had been missing on our boat, but we'd had it for over 10 years and never had an issue, but it doesn't mean it isn't possible. So for less than $75, it's good piece of mind that I won't have water coming up through the manifold. I'm sure the Sierra version is just fine, it looks like it just covers up a little but more. The flappers are designed to stop most of the water, not completely seal it off.

 

[pmergler]

Re: Mercruiser Exhaust Water Shutter

Excellent, thank you everyone for the thorough responses. I went ahead and decided on the OEM since I found a local dealer with them in stock for $64, plus I have a $15 credit with them. Plus, I was reading in some threads about people struggling to install some of these flapper replacements (from a fit standpoint). I don't know for sure but I am assuming the OEM will be a more precise fit.

And i agree....probably not critical, but for < $70 the piece of mind is well worth it as opposed to the other alternative

 

[chipp3rwood]

Re: Mercruiser Exhaust Water Shutter

please help me find a water shutter for a 1975 cobalt 302 mercruiser!!!!

it has a 3 inch water shutter that is a perfect circle.

not oval or oblong.

i cant find one any where.

many thanks
chip

 

[augie21]

Re: Mercruiser Exhaust Water Shutter

A couple of years ago I had to replace my motor after water rushed in through the exhaust. I would recommend replacing the water shutter.

 

[bigskiohio]

Re: Mercruiser Exhaust Water Shutter

My dealer also said not needed, he said putting the boat in the water the most possibility of trouble ,put boat in slow. so if you dont know if you have them or not ,slow

 

[jtybt]

Re: Mercruiser Exhaust Water Shutter

I have found the dealers in general are the least knowlegable and or mis-informed of the boating establishment...and that's being generous.

The shutters are MOST effective in a following sea with the motor off or when backing down a ramp. However, there are multiple causes why and how water can enter the exhaust manifolds and cylinders.

The first is of course the leaking manifold to riser joint. Second is the height of the engine in relation to the water line. Water coming in this way is sometimes call water reversion. Reversion can and does happen at idling simply from water exiting the riser so close to the exhaust.

Cam shafts are ground so the intake lobe and exhaust lobe 'overlap', meaning the exhaust valve is still in the closing stages when the intake valve is opening. This overlap causes a scavenging effect in the combustion chamber to suck out the last bit of exhaust and start the intake flow of fuel/air mixture a tag before the piston starts it's down stroke. This adds power. The thing is, during idle RPM's when this is all happening in comparatively slow motion, there is a sucking of the exhaust back into the combustion chamber. This suction also sucks the raw water as it's exiting the riser at a relatively close proximity to the exhaust tube of the riser.

 

[futz]

Re: Mercruiser Exhaust Water Shutter

Volvo does not recommend flappers/ shutters to be replaced when they go.

http://boatfix.com/new2.htm

 

[bigskiohio]

Re: Mercruiser Exhaust Water Shutter

by dealer i also should have said he is also a certified mech for 30 years or more.

 

[bascomechanic]

Re: Mercruiser Exhaust Water Shutter

Use oem parts only I have found other than quicksilver I have had problems with fitting and poor rubber made in china.