Y Tube Shutter "Flapper" Maintenance

[sr79]

79 Sea Ray 260HP - I installed a rebuilt sea water cooled 350 engine and set it up for fresh water cooling with heat exchanger. Log type exhaust manifolds are clean and I have a 145 degree thermostat. The engine slowly heats up to 195 degrees and stays there at 3100 RPM and cools down at lower RPMs. Water pump is new but, I didn't inspect the exhaust flapper. My question is: can anything go wrong with the flapper i.e. get stuck and work as a heat riser?

 

[GA_Boater]

Exhaust flap mounting hardware corrodes and flap can drop, partially blocking the exhaust

When you say water pump, the circulating pump or impeller? Water pump is often used to describe both.

 

[sr79]

I installed a new circulating pump and outdrive pump impeller. Are there any ways to inspect the flap without pulling the engine? Is the flap visible through the exhaust passage when the outdrive is removed?

 

[GA_Boater]

I haven't replaced a flapper on a V8 or V6, so I'll let the other guys answer that one, SR. But I think the hose can be worked out of the way to look at it, but again, not 100% sure.

I do know you can't easily see it through the Y pipe with the outdrive off. Maybe a mirror? Sometimes it ends up on top of the lower unit or in the exhaust passage in the lower.

 

[Bondo]

Are there any ways to inspect the flap without pulling the engine? Is the flap visible through the exhaust passage when the outdrive is removed?

Ayuh,..... The only way it's visable with the drive off, is if it burnt up, 'n fell down,....

To see 'em, or change 'em,...
Remove the elbow 'teen the exhaust riser, 'n the y-pipe,....
The shutters are right under the lower rubber boot on the downstream end of the elbow,....

Ya gotta loosen, 'n slide both rubber boots off the elbow to get it out,.....
A hose pick helps loosen 'em, 'n a squirt of Quicksilver Power Tune will make 'em slippery,....

 

[Mercruiser420]

Did you change the housing too or just the impeller? Sometimes the stainless cup will actually separate and spin inside the plastic housing with the impeller at high rpms causing your exact symptoms.

 

[sr79]

Yes, I changed the impeller housing (changed the complete kit) Also. if I removed the 2 raw water hoses from the heat exchanger going to the exhaust elbows with the engine running (boat in the water) should I expect to see a very large volume of hot water flow? Would this be a reasonable test to verify impeller efficiency?

As for the Y Tube flap, It is my understanding that the engine needs to be removed to access the flap on the older (1979) Mercruiser I/O's. Is this right?

 

[Mercruiser420]

If water is flowing out of the hose going to the riser your impeller is efficient and your system is clear, though I wouldn't run it more than a few seconds with the hose disconnected, you need constant water flow through your risers so you don't melt any boots.