Exhaust noise

outdoordad

Cadet
Joined
Oct 30, 2008
Messages
9
I have a 1997 stingray with a 3.0 mercruiser.
while running my boat i developed a knocking noise, after stoping and inspecting my engine. It sounds like i have an exhaust leak. When it idles it sounds like an old steam engine running. It still has plenty of power and starts up with no problems. I sprayed soapy water all over the manifold and boots but did not see any bubbles. Is there any other way i can find where the noise or leak is coming from?
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,308
Is there any other way i can find where the noise or leak is coming from?

Ayuh,...... Welcome Aboard,....... With the cold motor idling, run yer hand slowly along/ around the gasketed exhaust joints,....

When yer hand passes the leak, you'll know, as it's be extremely HOT in that area,.....
 

tank1949

Lieutenant Commander
Joined
Apr 4, 2013
Messages
1,911
Maybe where gases pass through boat. On V8s, a Y Pipe is bolted to a transom assemble, which sometimes leaks, expecially if boat is used in salt water. Good luck.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,348
Hi
Check one of your spark plugs haven’t come loose. Also check you haven’t blown a hole in your exhaust, perhaps even from frost damage over winter.
 

harringtondav

Commander
Joined
May 26, 2018
Messages
2,477
+1 to QBhoy's recommendation. I had a bad spark plug. The insulator was apparently cracked at the metal head. I noticed a knocking clicking noise. I slowly increased speed to observe any changes in sound. When I went to WOT throttle there was a bang, and then chuff-chuff. The insulator blew out of the spark plug body.
 
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