Yanmar Diesel

[regelitsu]

I don't know if this is the right place to write this but here I go. I just got a boat with a pair of Yanmar 6LY 440's and they are great engines. Very similiar to the old 12v. I just have this frustrating sound that seems like it is coming from the exhaust. Seems like a wastegate problem. Only happens when I let off the throttle. No miss or any abnormal engine operation. The catch is that I held the wastegate actuator closed and open and still got the sound. It sounds like a fluttering noise and occurs and any RPM when I let off and then sounds normal again. Engine does not overheat and has plenty of oil pressure. Engine actually operates just perfect. I guess the only was that is could be the wastegate flapping in there is if it broke of the lever that the actuator controls. Any ideas are extremely appreciated. Thaks.

 

[RustyJC]

Sounds like turbocharger compressor surge. Does it still "flutter" if you ease out of the throttles gradually?



Rusty

 

[EKlem]

Is it wet or dry exhaust? Wet exhaust can make some weird noises if you come out of it fast. Also, is it one engine or both?



Rusty's diagnosis seems like a good one. I have never heard a yanmar do that but I have only used them in applications where you don't cut the throttles real quickly.

 

[regelitsu]

This is under no load, so there is no boost. It is only happening to one of the engines, and it does have wet exhaust. I already dried it hoping it was that and that did not work either. As far as surge, I disconnected the pipe that goes to the aftercooler and it still did the same noise. Thanks for the relpies.

 

[RustyJC]

This is under no load, so there is no boost.

OK, that would have been good to know back in post #1. That, and the fact that it's only one engine, is somewhat strange.



Rusty

 

[DiTrani]

Yes, curious.



What's in the exhaust system between the turbo and the transom (assuming transom exit)? Anything fancy like surge tubes?



How easy would it be to swap the turbos to see if the sound swapped engines?

 

[regelitsu]

After the turbo there are two elbows. One does a 90 up and the other a 90 towards the back and into a straight pipe. The second elbow is the one that mixes the water and the goes straight out. I am going to try to see what happens after I change the turbos out. I am going to at least have to pull one of the turbos out to see what the heck is going on in there. Kinda strange huh?... .