Grinding noise

JPGator

Active Member
Apr 25, 2019
495
Treasure Coast
Boat Info
2008 Sundancer 40
Engines
Cummins QSB 5.9 425HO
’07 340 with 8.1’s

What kind of noise does an impeller make when it goes bad?

Departing the anchorage both engine started and stabilized. Then I noticed the port engine RPM’s act sporadic, paused the radio and listened to a clunking/grinding sound. Quickly placed the engine into neutral-no change. Tried reserve perhaps to free debris but nothing and then the engine quit. Limped home on one engine. Belts are fine, oil levels good. No over temps.

Thoughts or suggestions?
 
Since the impeller is rubber, I doubt you'll hear any noise. Yours sounds like something internal. Good luck.
 
Thanks. Guess I’m gonna need it.

Did the sounds seem to be coming from the engine interior or more outside? When it quit did it seem more like a lockup or turning off?

What was your alternator putting out and what is the status of your batteries? Perhaps the alternator let loose and stopped putting out voltage, when battery voltage drops the ECM will go offline and everything will shutdown.

Take if one step at a time unless you feel it's locked and an engine internal issue.

-Kevin
 
The engine RPM’s typically stabilize at 600. The engine started and automatically dropped to 300-400 with erratic changes. The grinding/clunking noise was hard to discern exactly where it was coming from but I’m thinking inside the engine bay. Engaging the engine into gear did nothing to change the rpms or stop the noise until she simply quit. There was no shaking so it didn’t fee like we ran over any debris.
 
There are a number of external components like the alternator that could fail. You said temps were good so we can probably skip the raw water pump for now. Since the engine shut down I start with examining the alternator and its output. If you did not charge the batteries overnight you could start there but if they were on the ac convertor then they'll probably show good even if the alternator was not charging.

-Kevin
 
Boats connected at the dock so that probably won’t work. I’m heading out to the boat shortly to take a look at things in the day light. If you think of anything else shoot me a text.
 
I have no earthly idea!

The boat started up just fine. Took videos of the belts and alternator and everything looks normal. Put the engine in gear, out of gear, reverse. Everything worked normal.

Next step is to take her out this afternoon.
 
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If your boat has V-drives the clunking was probably the transmission damper plate because the RPM were low due to a cylinder misfire or low rpm from a bad IAC valve.
 
If your boat has V-drives the clunking was probably the transmission damper plate because the RPM were low due to a cylinder misfire or low rpm from a bad IAC valve.

Is this a one time thing or something that needs to be fixed immediately.
 
How can I test it?

Internet says the idle should be higher if it failed. Mine seem to be what same when I started the boat this afternoon.
 
Not so. I'd replace it, common problem, sometimes it throws a code sometimes not. Good place to start.
 
Yesterday I went for a swim in our nasty marina to get a first hand look at the prop and shaft. Nothing was stuck or wedged around the shaft/prop and the prop itself had no damage. As for me time will determine whether that disgusting water kills me.
I started the engine again and it ran fine. No issues with the RPMs, temps or anything really and obviously the banging plate noise was not there. Took the boat out for a quick cruise in the no wake zone putting the engine in forward/reverse/neutral etc. Lots of turns, spins and not a hiccup.

This morning I spoke with my mechanic and he seems to think it was most likely something getting trapped in the prop which later freed itself on the way home. Had I done any significant damage the boat would run differently, which it doesn’t, and since all the engine parameters are normal there really isn’t anything much to do.

Anyhow, thoughts and opinions are always welcome.
 
Sounds like you may have dodged a bullet here. I would repeat the scenario of heading out to the open water and listed closely to everything. Get her out in the open and slowly increase RPMs and see what happens.
 

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