[njc15880]

I have a 2000 z272 with a 454 MPI and at cruising speeds, the engine is producing a whistling sound. It almost sounds like a belt squeal. However if you give it full throttle, or reduce throttle, the whistle goes away. I am thinking it's an intake or vacuum leak. I have inspected the top end of the motor and I can't see anything wrong. Does any org have any advice?

[ColoradoDiablo]

Try using a can of non-chlorinated brake cleaner around the intake.
Fire it up and just spray conservatively around the intake.
If you got a vacuum or intake leak you'll find it.
Also check and make sure you don't have a idler or tensioner pulley going bad.

[njc15880]

That's a good idea. Thank you. I did check the belt and all the pulleys. It all looked fine. I'll try that and see what I come up with.

[ColoradoDiablo]

Don't mean to step on your wrench turning skills , but
did you check the pulleys with the belt off? Alot of time it's hard to tell unless you can physically spin the bearing in the pulley by hand. Alternator bearings and even the P.S. bearings can raise he-- too.

Keep us posted

[njc15880]

Oh no sir you can step away hahahaha. Yes I pulled the belt off, checked for wobble and anything that felt like it was dragging. I put a new alternator and water pump on, for other reasons and nothing changed. The noise only happens user a load at cruising speeds. When I have it out of the water or in neutral I cannot make the whistle. If the brake cleaner doesn't work, my next option is to pull the seat out and pull everything I can apart and put it in the water.

[Hudson River Steve]

My 7.4 MPI was similarly whistling but it was due to the flame arrestor. I pulled it off and cleaned with brake cleaner but it still whistled. Turns out the aluminum fins were oxidized...needed to be replaced.

[ColoradoDiablo]

Hmmm ,
Gimble bearing , u joints maybe.
I think your right , you're going to have to pinpoint the area a little more.

[ColoradoDiablo]

Hmmm ,
that's interesting Steve. Gotta remember to check for that in the future.

[njc15880]

Steve, that was my first move. I cleaned the flame arrestor with brake clean and it didn't stop it. So I figured it wasn't that. I was going to replace it, but it's like 200 bucks. I think I'll pull it off and run the boat to be sure. Did you find a cheaper one?

[Hudson River Steve]

I did the same, clean with brake cleaner but closer inspection showed that it was corroded. Probably due to salt air...not sure if that is your problem.
The stock Mercruiser flame arrestor can be replaced with a higher flowing unit from K&N for much less than half the cost....win-win! 59-5004 - K&N Marine Products, Marine Flame Arrestor direct from K&N