exhaust water flow

[Thor]

I have 2001 Sundancer with 3126 Cats and seeing very little water coming out on the port side. The starboard side has a great flow and splash, the water on the port side barely running. I cleaned out the heat exchangers (had lot's of impeller pieces, 14 to be exact) and cleaned the transmission cooler which was 25 % clogged. To check the system I disconnected the 1 3/4 hose from the exhaust elbow and then hooked a discard hose to the raw water system. Even at idle it a tremendous amount of water coming out when testing, but as soon as I connect it to the exhaust, then just a trickle. I am aware of the underwater exhaust port, but this just does not look right. If I increase the RPM to 1000 I will have as much water coming out on the port side as the other engine at 600. Is there anything that could be blocking or preventing this flow? Thanks Thor

 

[dpmulvey]

Same problem here. Granted it's a gas engine. Some thought and what I went through.

Is there water in the oil? If not, get a Thermal Temp gun at HF and check that both engines are running at the same temp. That is more important than the amount of water comeing out right now. Unless the exhausts length, angles, condition, etc..... are exactly the same, you will have a difference in flow. Is the muffler clogged? Have you been under the boat to see if the water is being forced underwater? I was under the impression that worked more on suction than anything else. Have you checked all the hoses for clogs with a fiber optic camera? Is there a list in the boat to starboard? Did you get all the impeller pieces? Did you change both impellers at the same time? How are the Tstats?

 

[CRUZ'N]

Have you checked for a " stowaway " ? Did a visitor build a nest...?

 

[rondds]

Have you checked the current impellers? I know you found pieces but that may be from previous fried impellers. Try running something up into the exhaust (length of wire?) to check for obstruction.

 

[Alegria]

Not sure what type of collector you have. If it is a log type collector your water might be going out through the underwater exhaust when you up the rpm and water flow you get it going out both underwater and the side. I have read there could be a cover on the underwater side that has gone missing due to wear time overheat condition. Normally it will cause the log to fill up and dump overboard then when the boat is moving the flow of water over the underwater exhaust sucks the water out stopping the overboard discharge.

Can't really say for sure if the temps are normal I don't know the down side. One concern I have in my case is wondering if that change of water flow compromises the cooling system when you come down off plane and the temps rise how soon it recovers.

 

[Thor]

I just had the boat up on land and checked it underneath when I painted it, everything is fine there. And I do not have any problems with high temp when running it so it must be a good flow under water, it is just when sitting at the dock that I am surprised to see just a trickle. The impellers where just replaced and I know the raw water system up to the exhaust elbow is fine due to my test with a hose connected to the water pipe coming out of the transmission cooler just before the exhaust elbow. So the problem must be down stream from there. Not sure if it is a muffler that the side outlet hose is connected to? Could there be some kind of valve there? Thor

 

[Alegria]

On mine there is an in line muffler before the overboard discharge when I brought the boat the low flow was noted and the dealer investigated and replaced the muffler with a new one sighting that there were baffles in there and due to an earlier overheat condition the muffler became distorted restricting flow. I did not really know any better at the time and they were going to replace it on their dime so I did not question. That did not fix the water flow condition as it went from nothing at any rpm to like your condition now.

 

[Buckeye Kevin]

I had the exact same issue on my port 8.1 (previous boat) Tried everything you did and finally had the Merc tech come to the boat. He inspected everthing/ran the infra-red gun and all was well. He stated that at low RPM's the exhaust water will take the path of least resistance. At low idle that path was under water. At about 850 RPM's the waterflow is strong out the side. Ran for a season and a half with no issues at all.

 

[Thor]

I see that they call it a muffler for gas boats, and bypass expansion chamber for the diesel boats. I had so many broken impeller pieces in my heat exchanger that it is possible the expansion chamber got overheated, though I never had the engine over heat. I am sure the expansion chamber is expensive, and I hate replacing it if I don't have a valid problem. If there are baffles in it, I guess they could be damaged with to much heat. Any one out there that know how the expansion chamber is built or have a suggestion? Thor

 

[Turkanon]

Have same issue on 2003 410 with 3126 cats. Not overheating, very little water being pushed out bypass On both sides at idle or at cursing speed. Was low when I had Survay done. 755 hours. Boat runs fine, but people comment on it all the time making me wonder if I should be worried. My questions are:
1) What is the reason the bypass expansion chamber is installed?
2) Does no water coming out mean they are damaged?
3) Can a damaged Exhaust By-Pass Expansion Chamber limit performance or damage the engine?
4) What does it look like inside?
5) How much do they cost to be replaced?
6) If the boat is performing ok, and it causes no damage, is it worth the time and expense for me to see water come out the side of the boat?
I see further up the thread that Algeria had his replaced on the Dealers dime and sees no difference.
Appreciate any input.