Underwater exhaust question

roosevelt14

roosevelt14

Well-Known Member
Apr 15, 2007
596
Western Lake Superior
Boat Info
2002 450 Express Bridge
Engines
Cummins 6CTA 430hp ZF280IV
At what RPM does the underwater exhaust kick in????

On my (new to me) 2002 360 with the 8.1, I have yet to see the exhaust exit the bottom of the boat! It comes out the side like a fire hose at cruise... I still run at 160 temp both engines at cruise (3600 RPM)... Is there something stuck in the exhaust cans?? Can they be taken apart??? Cleaned?? This boat was in salt water before I bought it....but now is run in fresh water... Any Ideas...
 
You will always have some water and exhaust comming out of the ports on the hull sides at the water line. These ports are actually bypasses for the exhaust system. At idle most of the water and exhaust will come out of the bypasses. At speed the drag of the water running past the underwater exhaust outlets actually pulls the exhaust and water into the wake. They are working, you just dont see them.
 
Agree with the assessment that you will not see exhaust come out at cruise from beneath the boat. The side exhausts on my Crusaders send out more of a mist than a fire hose type of discharge. If you are running at 160 degrees you are right on the money. If you are not smelling exhaust, also good.
 
sorry to revive an old thread, I'm having the opposite problem on my New to Me 2003 Sundancer 360. Port engine exhaust at idle is all coming out underneath, no water is coming out on the hole above the water line. STB engine exhaust is coming out the exhaust hole. Ran it 3500 rpm for 3.5 hours, no issues, all temps are fine. Any ideas why the exhaust at idle would only be coming out my underwater one?
 
At idle, sitting at the dock, the water should exit the above water exhaust because there isn't enough pressure to fight the pressure in the below water exhaust torpedo. That pressure is essentially equal to the draft of the boat. In my case, 40" of water. 407 inches of water column is equal to 1 atmosphere, or 14.7 psia. The reason that there is an above water exhaust, is so the cooling water and exhaust gases can bypass to the above water exhaust without imparting a big back pressure on the engine.

With the engine idling at the dock, and no water coming out of the above water exhaust, can you hear "bubbling" from underneath the hull? Said another way, at the above water port, there is no water, so there shouldn't be any gases either. Is this your case?

Just trying to think through this.
 
at idle at the dock there's an abundance of bubbling on that engine coming up from the underwater exhaust. other engine has none and has good water flow out of the above water exhaust.
 
So something is clogging the bypass (above water discharge/exhaust) to such an extent that the exhaust is finding its way to the underwater discharge, and bucking the pressure exerted by the draft of your boat. It has to be that. Can you take off the bypass portion of the exhaust hose and really inspect it?

Also, and this is not to be a demeaning questions, but are you sure that you stuck the coat hanger in the right above water exhaust port? On my 420, on the port side, the generator and the port above water exhaust are right next to each other. I believe that my generator exhaust port is a tad bit smaller in diameter. Again, just thinking out loud.

Jaybeaux
 
I
rhymeandreasons said:
sorry to revive an old thread, I'm having the opposite problem on my New to Me 2003 Sundancer 360. Port engine exhaust at idle is all coming out underneath, no water is coming out on the hole above the water line. STB engine exhaust is coming out the exhaust hole. Ran it 3500 rpm for 3.5 hours, no issues, all temps are fine. Any ideas why the exhaust at idle would only be coming out my underwater one?
Click to expand...
I had the same problem. Stuck an electrical wall fish in there & partially dislodged what looked like a birds nest. Then went for a ride & hit WOT for a few minutes & problem was solved.
 
rhymeandreasons.....here is a picture from the manual for my exhaust....the highlighted #1 is the above water exhaust we are talking about. I know that you know this. Just for demonstration purposes.
 

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Jaybeaux said:
So something is clogging the bypass (above water discharge/exhaust) to such an extent that the exhaust is finding its way to the underwater discharge, and bucking the pressure exerted by the draft of your boat. It has to be that. Can you take off the bypass portion of the exhaust hose and really inspect it?

Also, and this is not to be a demeaning questions, but are you sure that you stuck the coat hanger in the right above water exhaust port? On my 420, on the port side, the generator and the port above water exhaust are right next to each other. I believe that my generator exhaust port is a tad bit smaller in diameter. Again, just thinking out loud.

Jaybeaux
Click to expand...
On the 360, the genny exhaust is on the starboard side.
I believe on the 360 the above water exhaust hose is fairly long. Check to see if it's not somehow kinked. It's also fairly easy to reach, you might want to pull the end off of the muffler and see if you can blow thru it or even try a garden hose down it.
 
This is a starboard water lift muffler from a 340DA with 8.1s (It's been disconnected and twisted back to allow access to the raw water pump.). My 360 is almost identical with the exception of having a little more room.
The exhaust bypass hose is smack dab in the middle of the pic, normally connected to the back of the muffler. You can see how long it is and the hanger may not have been long enough to check for obstructions.

Remove the two hose clamps, pull the hose and check for a clog.

(Snagged this pic from the "How to change impellers" thread: http://www.clubsearay.com/index.php?threads/how-to-change-impellers-in-8-1s-with-pictures.26440/


013.jpg
 
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