Wow, sure great read. I immediately jumped in and pulled my plugs for a read, my issue isn't oil related as the plugs definitely don't show oil burn. Waiting to hear back from Wipple on a possible reflash to address the issue.

Thanks

Simple Green or Spray Nine works well, and much less harmful.

I always have a little bit of soot after long days on the water, but it's manageable.
There was a factory reprogram or PCM replacement, for these motors back in the day.

Call your local dealer with your Engine S/N, and see if anything was ever done to your engine.
If not, you still may be eligible.

+1

My last boat was a 2003 Sonic with twin 496HO's. It also made a ton of soot on the transom. I had the ECM's updated with the latest factory program and the soot was mostly gone. It was something to due with incorrect voltage readings IIRC.

Paint transom. With a painted transom the clear coat makes it much easier to wipe off soot (like a magic erase board). Some will even go black or gray with transom paint. I went white and wipes right off.

Otherwise, the soot gets in the pores of the gel and is a ***** to get cleaned off. Even with Simple Green.

here are the facts in the matter of the 496 one is Mercruiser thru P/A had a field campaign back in 2003 and early 2004 for soot on the transom. Swim platforms made it worse as it held the exhaust in the area no matter how fast you went on the water. (negitive pressure under the swim platform) The deal was to send your PCM 555 in and you would get a recal back with an IAC Muffler taped to the PCM as well. Mercruiser raise the pulsed width modulation of the IAC to allow more air at idle speeds and just off idle until the IAC does not come into play for the air side of it. (jist info) this helped as well for soot among a bit better fuel mapping curve recal into it.

with that said CALL mercruiser with your engine serial number and have all the numbers ready that are on the PCM if needed.. They can tell if the recal was done or not.

Next with that said around 2005 or early 2006 GM changed the intake gaskets to a way better sealing design. the sealing surface was alot better. The earlier ones where wimpy and I strongly recommend changing them to the newer design. This also caused alot more oil consumption ( the first gen intake gaskets did) hence more soot on the transom. Also by the design of the positive crank ventilation not external ( like all others) under the intake area caused oil consumption and soot as well.

I apologize if some one already stated this -

Getting the soot off -- Simple Green -- best stuff ever

Reason for the soot -- I have a 7.4 MIP -- Bravo 3 Captains Call exhaust all stock -- I thought I was doing the engine a favor and put in high octane fuel - the 93?? stuff from the gas station -- WRONG. I had more soot than you could shake a stick at -- I cleaned the transom off -- with Simple Green - put a good coat of wax on and the next fill used plain jane 87 octane -- No soot, no hit runs or errors.

Hope this helps

3pointstar

Rain-x the transom, soot won't stick. That's what i do on the front of boats and enclosed trailers when towing them with my deleted cummins truck, it works great the soot wipes right off

Clean it with vinegar. Apply a quick coat of wax. Next time it should come off easily with soap and water. Then quick wax again. The vinegar cleans the exhaust tips nicely too.

If using vinegar dont forget to re-wax after or the stuff will stick that much worse the next time. a good kitchen soap should get most of the stuff off anything remaining should come off during the wax process. My 02 can get pretty ugly after a day but usually comes right off but the soap will strip the wax as well. Not sure what simple green and some of the other cleaners will do to your gellcoatover time.
I live here in Fresno, Whipple just down the road from my work. I have thought about having them do a stage 2 flash on my boat for some time but its not cheap then stuck running 91 octain fuel. you can also send your ECM to Mercury for an updated flash. i have been told that helps if you have an early tune. Good luck.

I also wonder if longer exhaust tips would help this. There was a post not to long ago with one of the members changing out stock exhaust tips (5 in) i believe for longer ( 10 in ) if not mistaken. Im wondering if the exhaust being further from the boat would help.
For what its worth a very good friend has a 29 fountain (525 blue motor) that is worse than my boat is for soot. I believe the boat is mid 2000 or so.