New engine noise from wet exhaust

colinb

.
Aug 4, 2021
6
Roberts Ketch offshore ketch gold coast
I have a Kohler genset with wet exhaust exits through the transom. Runs well everyday. Suddenly after start up I can now hear engine run sound through the wet exhaust that I have never heard before. I have checked both sea strainer and impeller to ensure no raw water flow issues. Engine oil level good and 100 hours from last service
Wet exhaust flow appears normal ?
Any thoughts please
 

colinb

.
Aug 4, 2021
6
Roberts Ketch offshore ketch gold coast
Low water level in your muffler. Possible small leak would drain that muffler level.
Jim...
Thanks Jim, great thinking. I will investigate tomorrow. As you would guess Kohler is in a tight space in the Lazerrette. Exhaust side hard up against the hull. Very little space.
No sign of any leak under genset as it drains into clean section of hull to bilge. Will let you know how I go
Thanks again
 
Dec 28, 2015
1,357
Laser, Hunter H30 Cherubini Tacoma
Has the weight distribution changed in the boat? I had a like situation and dismissed a water issue being my “pee” outlet showed water coming from it on my stearin. Turns out the elbow for the water injection on the exhaust elbow was clogged forcing all of the cooling water out of the “pee” outlet and none was going through the exhaust. I have a vacuum break elbow between the heat exchanger and exhaust elbow that had a hose plumbed into the top of it that exits through a through hole on the stern. This allows me to verify water is pumping but in this case, water was pumping but not getting to where it needed to get to.
 

colinb

.
Aug 4, 2021
6
Roberts Ketch offshore ketch gold coast
Hi All, just inspected exhaust side of genset. Muffler looks and sounds ok. Heated raw water from heat exchanger flows into top of exhaust elbow cleanly.
Having run genset again I now agree ejected wet exhaust from transom is perhaps 30% down and only shoots out 2/3 of what I recall it used to. I am beginning to suspect Heat Exchanger restriction as likely candidate. Thoughts please. Heat exchanger replaced 4 years ago as coolant was leaking internally mixing into raw water. Coolant still good at this point
Thanks all
 
Feb 14, 2014
5,714
Hunter 430 Waveland, MS
I am beginning to suspect Heat Exchanger restriction [HE]
I have a 9KW Kohler.
My water pump is not a flex vane type, which is the type that fails and put rubber parts in front of the HE, thus blocking flow.
What is your Model Kohler?
Jim...
 

colinb

.
Aug 4, 2021
6
Roberts Ketch offshore ketch gold coast
Hi Jim
Kohler 6.5EFOZD
Regularly change anode every service 250 hours. Never had a failed /broken flex impeller. Pump is rotating freely and belt tension good.
Somehow I need to check flow in the system. Yacht just antifould 3 months. Raw water gushed in at last strainer clean(quick open close) . Remarkably exhaust elbow very clean and pure white paint no sign of any overheat yet raw water inlet into mixer only 3/4 inch into 2 1/2 inch exhaust mix elbow.
Surprisingly to me, muffler feeds into 2/ 1/2 inch rubber tube which rises at least 2 feet then travels horizontal for 3 feet before dropping 2 feet to transom elbow outlet.
Question: engine exhaust gas must pressurise mixed flow for it to travel that distance. ?
 
Feb 14, 2014
5,714
Hunter 430 Waveland, MS
Surprisingly to me, muffler feeds into 2/ 1/2 inch rubber tube which rises at least 2 feet then travels horizontal for 3 feet before dropping 2 feet to transom elbow outlet.
That loop is needed for the heel on sailing, but normally the exhaust is high enough above the water line to prevent back flow.
_____
Question: engine exhaust gas must pressurise mixed flow for it to travel that distance. ?
Answer is Yes. This causes the "spitting" or bursts of water, as your Genset engine Blows it out.

Perhaps your Muffler has crap it.
To hear the engine sounds, the muffler must not be filling with enough water.

Here is a picture of mine that was dunked for 10 minutes from Hurricane damage. I will get a new one by insurance.;)
So ignore the dirty state...
Muffler.jpg


The Muffler is not a big thing, but hard to disconnect and clean.
You might Disconnect the hose at Riser and run a endoscope camera to see inside it, or disconnect that Loop and flush the Muffler clean with water hose.
Jim...
 
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colinb

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Aug 4, 2021
6
Roberts Ketch offshore ketch gold coast
Thanks Jim, appreciate your time here.
Going back to basics. My raw water feed into exhaust elbow is the same as yours.
I am going to undo at this point. Crank engine to see flow into a bucket or similar. If I can tell it’s good maybe muffler is contaminated or blocked. I suspect flow will be weak and I have a blocked or contaminated heat exchanger. Mine can be disassembled but messy job to do as you lose all coolant and a pain to get at
 
Feb 14, 2014
5,714
Hunter 430 Waveland, MS
Your engine will get hot fast too.
If you want to check this out..
do the Riser flush with water hose. It may be possible to connect water hose to the exit hose with a pvc pipe adapter.
This would flush the entire exhaust loop and check for crap flowing out.
Jim...
 

colinb

.
Aug 4, 2021
6
Roberts Ketch offshore ketch gold coast
Thanks Jim, I have used Colburn for a while. Even with fix rate and freight a third of Australian Kohler parts prices
I was going to cap the disconect on the exhaust elbow and just crank for ten seconds and check flow from HE
 
Jun 18, 2015
27
Mascot 28 Pilothouse Motorsailer Grand Manan
My exhaust hose collapsed internally,from age, & partially blocked exhaust.