Bravo 3 exhaust issues?

[ni7irs]

I just replaced my lower unit with a factory reman. When I tested it with the muffs on, no exhaust or water coming through prop. I used to remember at least some steam from the prop.

With the boat in the water, there is a purring sound almost like all of the exhaust is coming out of the vents near the upper unit. Did Merc send me the wrong lower unit? I didnt see anything that I could have screwed up in the connection between the lower and upper housing.

Any comments welcome. Thanks!

 

[Bondo]

Re: Bravo 3 exhaust issues?

Ayuh,... My guess is the shutters got burnt up from a lack of water flow, 'n dropped down into the bottom of the Y-pipe, causing what yer seein'...

 

[ni7irs]

Re: Bravo 3 exhaust issues?

There is also a knocking sound in the engine at idle that is not there if it revs up. Is that consistent with the shutters dropping?

Is it possible that Merc sent me the wrong lower unit? I didnt see the way that exhaust can come out of the prop area. It looked pretty well sealed to me, but Im not an engineer.

PS - This was not a voluntary DIY. Mechanic wanted to sell me his rebuilt lower unit for $3,700 with a 90 day warranty and Mercruiser said their rebuilt with 3 year warranty was $2,800. He refused to install the Merc unit and handed me a box of parts. Certified Merc mechanic didnt want to touch it (understandably).

 

[Don S]

Re: Bravo 3 exhaust issues?

If you have the bow of the boat down and the drive slightly up, you probably won't get any water out of the prop. It will all drain out of the idle relief ports at the base of the gimbal housing. And if you have an exhaust tube other than the bellows, more water will drain out the tube.
If your raw water pump is getting on in age (over 2 years old) it's also probably not putting out as much water as it should.

Knocking is another thing all together. Is it knocking or ticking? big difference. If you hear a ticking sound like metal lightly hitting metal near the exhaust Y pipe, it probably is the shutters with the rubber coating burned off from lack of water moving back and forth inside the Y pipe..
A cheap mechanics stethoscope will help you locate where the "Knocking" is coming from.

 

[ni7irs]

Re: Bravo 3 exhaust issues?

I would say more than ticking, more like a clunking as the engine turns over, but only at low idle.

 

[Don S]

Re: Bravo 3 exhaust issues?

Get the stethoscope and determine where the noise is coming from.

 

[ni7irs]

Re: Bravo 3 exhaust issues?

I should still replace the shutters though, right?

 

[Don S]

Re: Bravo 3 exhaust issues?

If they are bad, yes replace them. If not bad, why replace good parts.

PS: If the rubber coating is burned off, they are bad.

 

[ni7irs]

Re: Bravo 3 exhaust issues?

Got it thanks!