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rhythmic hiss at idle... valve blowby? Gasket? Belt? Injector? Water pump?


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Calling @Woodski

Trying to determine whether this sound is something I need to worry about or not.

Mechanic stethoscope on the way to help diagnose but wondering if anyone knows what I should look for.

 

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Posted (edited)

Headphones might help. It's pretty obvious in the boat. About 4-5 hisses per second at 650 RPM idle. 

Should add it seemingly only happens with the engine warmed up. 

Edited by UWSkier
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My vote is belt. I have the same noise and it's also temperature dependent. I had to buy a belt in a pinch at an Orielly's a couple seasons ago and the V was just a little too wide so it sat up in the pulley grooves a bit. I think as it started to wear down it started making that noise. Try tightening a bit or replace if it's been a while. 

Edited by drh
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I had a weird whistle at start up and some low RPMs on our txi, it was an exhaust hose clamp. 
 

(Disclaimer - I didn’t listen to the video, just something else to check)

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@UWSkier - the only hiss I hear is the smoke coming out my ears watching a skier get up behind your boat as I look out at snowflakes from my office window....

From what I can hear in the video, agree that is sounds like belt chirp or some front dress item chirping.  You should be able to isolate the location with the doghouse up or with the stethoscope.  What type of front dress belt do you have, V belt or serpentine style?  Might be solved with a new belt or if the V style a slight tightening.

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I'll do some more digging but the part that worries me is the frequency. About 5x per second at 650 rpm is exactly how many compression strokes per second each cylinder should see. 

It's a v belt. Tightened last fall when I replaced the alternator but I have the old style bracket which is prone to fail. Will check that too. 

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@UWSkier - stick your ear or the mic near the throttle body and see if it is coming from there.  If it is, time for a leak down test to determine health of head gasket or valve seats.  Is the sound in your opinion a chirp or more of a crackle/hiss?  Chirp = belt, crackle/hiss = combustion noise.

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Have you checked the breather hoses?   I had a similar sound when I started it up for the first time.    Turned out I forgot to connect one breather hose after installing cleaned injectors. 

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21 minutes ago, Woodski said:

@UWSkier - stick your ear or the mic near the throttle body and see if it is coming from there.  If it is, time for a leak down test to determine health of head gasket or valve seats.  Is the sound in your opinion a chirp or more of a crackle/hiss?  Chirp = belt, crackle/hiss = combustion noise.

I'd call it a hiss.

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If a steady and constant hiss, no issues as that is normal intake noise (should have noted that).  If a crackle or stuttering sound, then you might want to dig a bit deeper.  Hard to communicate via wording v. making the noise itself, LOL!

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I'm surprised you guys can't make out that sound.  Maybe it's just because I know what I'm listening for.

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12 minutes ago, UWSkier said:

I'm surprised you guys can't make out that sound.  Maybe it's just because I know what I'm listening for.

Or it is a normal boat sound ;)

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Rereading the thread, remove the belt and see if the noise goes away based on alternator change.  Just don't run it too long as circ pump is now not spinning but should be fine for a few minutes at idle with the raw water pump still pumping.  Also, see if you can pinpoint closer to where the noise is coming from, as much as I move my head around the screen the noise keeps coming out of the speaker :whistle:

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22 hours ago, UWSkier said:

Mechanic stethoscope on the way to help diagnose

Just use a dowel.  Put your thumb over the end and cram the knuckle of that thumb into the bone behind your ear.  Move the stick around on the engine and pick out the distinct sounds.  Theoretically, you should also be able to hold your phone against the dowel so we can hear it when you find it.

  • Like 3
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Belt noise. No observable broken alternator bracket. Alt pulley seems to be true. Weird it just sort of came on relatively recently. 

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