496 Whistle

Ezgoin

I've got the rear seat-back off of my 262 Captiva while doing some trouble shooting.   When testing the engine, the intake suction noise at anything above idle is defening.  Sounds like it'd suck the shirt right off your back if you got too close, but I assume it's just an 8.1 liter drawing a ton of air.  The thing I'm not sure about is that when you begin bringing the RPMs up under load, a high pitched whistle developes that just screems as the RPMs come up.  Is this typical?

I understand that with the engine area opened up everyting will be louder, but the high pitched screem doesn't seem normal.  Any ideas?  By the way, the original owner apparently took the spark arrester off and installed a large K&N air filter in it's place so there is no spark arrester.

My other thought is... how on earth does that big block get all the air it obviously wants when stuffed into the closed up engine compartment?  The top of the intake is coverd by the plastic engine cover, when installed, and stuffed up against the back of the rear seat-back when everything is in place.  Where is it getting the air it needs/wants?

MarkB

Aren't there engine compartment vents under your gunwales?

LaRea

No, not typical at all.  Could the squeal be coming from a loose serpentine belt?  

212rowboat

Big engines or boosted engines will whistle if there is something obstructing the intake. To determine if it is a venturi effect obstruction, simply place your hand on the filter and see if it alters. And get that k&n off there. The coast guard will eat you for a snack.

Other things that will whistle are map/maf's.. if you have an o2 sensor monitoring, they are notorious for whistling. More of a howl, actually. It's because the cage is clogged.. which means it's time for a new one/set, depending if it's monitoring both banks or if each is being monitored.

And... Your engine was engineered with a lot more science than marketing... K&n studies marketing, not engineering. There are applications that work, but k&n is rarely one of them. Google for "no limit intake"... That'll solve your breath issue, but it won't stop the coast guard from putting condiments on your fun day and munching you good if they catch you.

Black_Diamond

++ on that K&N. That is just trouble waiting to happen. Get the OEM spark arrestor in place.

Ezgoin

Yes, there are vents/air intakes, but they are aft of the engine and pretty tight/restricted. Hard to imagine that's all the cool air intake that engine gets!

Definitely not belt sqeal. It's air noise for sure!

I knew the air filter is an issue, even though I am a believer in K&N filters, I know the spark arrester needs to be there for safety if nothing else! Have to see if I can find one somewhere. Any ideas? Are they readily available?

Nothing surprises me with this boat at this point! It's been one issue after another since I got it a few weeks ago! Some day soon I'll tell you all the story and make sure I mention the players!

Ezgoin

Hummm...I just did a search for a Mercruiser 496 flame arester and first thing that comes up is a K&N 59-5005 that looks exactly like what I have. Says its Marine Approved and meets SAE J1938 Standards.

212rowboat

If you're dead set on a k&n, at least run a dry one... Not an oiled one.. 

craigswardmtb

My 496 whistles a bit as well. Merc actually installs a little foam "filter" in the throttle body. It is known to fall out or get out of alignment. It's only purpose is to quiet the whistle. It doesn't bother me and in my mind if not there it is one less thing that could create an issue by getting sucked up. So I leave it alone and deal with the mild whistle.

bluto

Do some research.... K&N does make USCG approved spark arresting air filters. I'm also a big fan of K&N filters, both air and oil.

http://www.knfilters.com/marine/flamearrester.aspx

Dream_Inn

Yes, Craig hit it perfectly!  I'd almost guarantee it's that little piece of foam & hard to believe it until you hear the difference.  I had it happen to me on my prior boat.  Had the whistle for years, then I replaced that foam and it was gone.  I even pulled it back out to hear it come back.

Ezgoin

So where is the foam located? I've cleaned the throttle body flap and surrounding area and didn't see anything like that.
The whistle I'm getting is very loud, but as I said, I have the front of the engine open so everything is loud.

Ezgoin

I didn't think K&N made a filter designed to run dry.

Dream_Inn

it would be item #6 in this drawing (cheapest part I've ever done on a boat)...

http://www.marinepartsplus.com/catalog/mercruiser/serial/350_MAG_MPI_HORIZON_ALPHA-BRAVO/884717002/11681-100

If you put this "mercruiser foam piece in throttle body" into Google, you'll find lots of info on it as well.  Oh, and it's called an IAC muffler (goes in idle air control valve).

Ezgoin

Thanks for all the info. From all I've read on it I think my whisle/ shreak is worse than that caused by a missing muffler foam but I'm gonna try it anyway!

Just wondering.....if it's common for them to fall out....where do they go? Through the throttle body? That can't be good!

Ezgoin

Ok, so I installed the interior back into the boat including the engine cover and rear seat back which enclosed the engine.  What a huge difference in engine sounds!  Seems quiet as a church mouse now compared to what it was like with the front cover removed.  All those crazy air sucking and whisling noises are now subdued and quiet!  No wonder the front cover is 2" think plywood under the upholstery!

I can still hear the whistle, but way less obvious.  I did check for the IAC Muffler and it is missing, so I'm hoping when I get one and install it, the whistling will be reduced even further.

Thanks for all your input.

Dream_Inn

Yep, Install that muffler and whistle will be no more!  Glad sounds have dampened as well.