IAC whistle

[HallOfDreams]

Has anyone managed to cure the infamous 8.1 Merc 496 IAC whistle? I have asked my Marina to check/replace the filters. Any other tips?
Thanks
Michael

 

[Fun Times]

@HallOfDreams ,At what RPM do you hear the whistle? At idle or around 3000ish RPM?

If at high RPM, can you take a picture of the inside of the throttle body plate with the flame arrestor removed.

 

[HallOfDreams]

Thanks for reply. Boat now out for winter but whistle is on both engines and 1700 to 2500+ bodies are fine and I have replaced the IAC mufflers but did not get a chance to run prior to closure. The marine service manager did say that the mufflers would not cause it as the IAC is not doing anything at that RPM so I am thinking flame arresters although very clean.

 

[sbw1]

I always thought it was kind of a neat sound.

 

[Fun Times]

The whistle sounds have been known to come from one of two places on the 8.1 throttle bodies at any given RPM really...One being the hole where the IAC foam muffler goes circled in red in the image below which could very well been your issue...

If it turns out it's not then being your boat is around 2003/04ish year model then the other chance for the whistle sound could be because your throttle body opening "Plate" may not have had any Air Diverters mounted to the TB Plate....One Diverter on each side seen if you open the throttle all the way with the engine off of course .

Back in early 2005 I helped the Mercruiser field representative locate the whistle on a 25ft Cobalt which lead to the air diverters being mounted to the TB Plate like seen in the image below where the bottom part of the red circle covers/ends just above the mounting screw.

Mercruiser made a manufacturer running change by adding the diverter after we found the issue but no service bulletins, etc. about it that I saw anyways.

The lower torques screw head you see holds the back side air diverter on.

Next time you're in your boat, pull the flame arrestor and see if you have the diverter as yours may not. And if safely possible while under way and someone else driving, try putting your finger all around the "Plate" 'opening of the throttle body housing to see if the whistle goes away.

If the sound does diminish then you may need/want a new throttle body to stop the sound as they should come with the new diverter mounted to the plate.

Hope this helps, good luck.

https://www.justanswer.com/boat/5acia-just-bought-used-chaparral-sunesta-8-1l-dp-took.html

 

[Jeff Harrison]

The whistle sounds have been known to come from one of two places on the 8.1 throttle bodies at any given RPM really...One being the hole where the IAC foam muffler goes circled in red in the image below which could very well been your issue...

If it turns out it's not then being your boat is around 2003/04ish year model then the other chance for the whistle sound could be because your throttle body opening "Plate" may not have had any Air Diverters mounted to the TB Plate....One Diverter on each side seen if you open the throttle all the way with the engine off of course .

Back in early 2005 I helped the Mercruiser field representative locate the whistle on a 25ft Cobalt which lead to the air diverters being mounted to the TB Plate like seen in the image below where the bottom part of the red circle covers/ends just above the mounting screw.

Mercruiser made a manufacturer running change by adding the diverter after we found the issue but no service bulletins, etc. about it that I saw anyways.

The lower torques screw head you see holds the back side air diverter on.

Next time you're in your boat, pull the flame arrestor and see if you have the diverter as yours may not. And if safely possible while under way and someone else driving, try putting your finger all around the "Plate" 'opening of the throttle body housing to see if the whistle goes away.

If the sound does diminish then you may need/want a new throttle body to stop the sound as they should come with the new diverter mounted to the plate.

Hope this helps, good luck.

https://www.justanswer.com/boat/5acia-just-bought-used-chaparral-sunesta-8-1l-dp-took.html

This is interesting. My boat was re-powered with 2006 8.1’s by PO. My port engine does the Darth Vader suction noise at idle, and surges slightly but the strb engine is silent. I pulled off the flame arrestors, and noticed that the strb throttle body has these diverters, but the port does not. I wonder if these have any other effect on performance, strb engine seems to rev a bit higher than port. Can these be added or would I need to buy a new throttle body?

 

[Fun Times]

If possible, Post both engine serial numbers to see if maybe there looks to be a difference somewhere...Maybe ones a Base model and the others an HO (High Output)? Just a quick thought.

Also look at the throttle body plates for a small hole drilled through or not...The HO needed extra air to keep it idling better while the Base did not need the extra hole.

Notice 2 part numbers for item #1, https://www.mercruiserparts.com/bam/subassembly/31824/11414/70
496 MAG (Base Model)
496 MAG (H.O. Model)

To my knowledge there are no know part numbers for the diverters or holding "hardware" listed in a engine parts catalog put out to dealers for self installation later on... it's just something Merc added to the TB's in house though most likely they do have a part number somewhere to keep track of things internally.

The diverters had no effect on the overall engine performance though...Just helped with odd whistle sound noises around cruise RPM.

If desired maybe call or send Merc an Email so someone in customer assistance could try asking the right person for help of locating a part number/s to get back to you later on with...,https://www.mercurymarine.com/en/ca/contact/mercruiser-customer-assistance

 

[Fun Times]

My boat was re-powered with 2006 8.1’s

Look for serial numbers just above the engine starter along with on top of the engine decals.
https://www.perfprotech.com/blog/articles/mercruiser-serial-numbers

 

[Jeff Harrison]

Look for serial numbers just above the engine starter along with on top of the engine decals.
https://www.perfprotech.com/blog/articles/mercruiser-serial-numbers

Thanks for the info! They are the 8.1 horizon’s. I will grab the serial numbers off the blocks and post them. Pretty sure they were remans, maybe one was newer than the other.