Loud Whistling Noise

[cby7715]

I have a 4.3 Mercruiser in a 96' Proline 190. The motor runs great, but last time I took it out, it started making a loud, high pitched whistling noise when I turn the key. It does it when I turn the key to the "on" position. I don't even have to be trying to start it. It will continue the noise until I put it into gear and start moving forward. I've done some googling, and most people say it's some sort of intake leak or air leak?

The motor runs fine. The noise is just annoying and very unpleasant. Any ideas on how to fix/eliminate the noise?

[231CALIFORNIA]

If engine not turning over, its not an intake or air leak as there is no manifold vaccum until engine is running. cant you localize the sound just by listening?  if you have fuel injection an electric fule pump can make a whir sound but likely wouldnt go away very regularly. do you have a warning system with an under dash alarm for high temp, low oil pressure,low gear lube etc??  that should sound when key on engine off but it should have been there since new. my 96 merc bravo has one.  bilge alarm? just turn key one and follow the sound?
intake whistles happen at low throtle settings , often throttle shafts or other apendages of intake  but they go away normally as engine vacuum drops on accel and return when load is reduced again.
let us know what you find.

[cby7715]

The noise is coming from a small, black plastic cylinder that is wired in-line going into the back of the oil gauge on my console. I assume it's some kind of oil level/pressure alarm? I checked the oil, and the dip stick says its full, so does that mean it lost oil pressure?

The engine starts right up and runs fine even with the noise blaring. What do I do next? Take it to the shop to have it looked at?

[231CALIFORNIA]

sounds like alarm, chedk the temp sensor wiring and connection at engine near thermostat likely, check the oil press sending unit wiring and terminal , and if it has an inboard drive lube oil fill reservior check its level sensor as well, one of them is sending a warning propbably.
check a manual to see if they are normally open or normally closed switches
often the water temp is open until hot threshold is reached, the oil pres is closed until pressure opens it and the lube reservior if any has a float switch that is normally open a nd closes if level drops.
on 2strk  outboards there is also a 2stroke oil reservior sensor that
that can sound the alarm also.

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