Soot on transom area.
 

Does anyone else have to wash soot of the transom area after each use?:( It is not heavy but more than I would think should be normal. I have searched the forums but don’t find much. I read one that said running 87octane (which I do) will sometimes affect the anti-knock/ping sensor to make a engine run rich, thus producing soot. Another said to use injector cleaner. That’s about all I have found. I welcome any advice since I am inept when it comes to the workings of an engine. :confused:It runs fine and no hesitation on the throttle. It does have a loud air sucking sound at certain idle speeds. It’s a Merc 496 HO.
Thanks in advance!

you could have a vacuum leak causing improper air/fuel ratio, but I would think that would cause a slight hesitation. On the hiss, I would guess a vacuum leak. Look around the engine compatment while engine is running to identify where its coming.

Mercruiser recommends 87 octane for all their engines, I can't imagine that'd be a result. One of our other members asked me about soot from the exhaust ports on his 496, so it sounds like it could be a common problem. I recommended fuel injector cleaner, or possibly a SeaFoam treatment.

Thanks for the info guys. I will put in some injecter cleaner and check for a leak next time out. Like I said, its not bad, but the old 5.7L had hardly any sooting at all. At idle speed a small amount of exhust and water comes out of thu-hull pipes all the time. This maybe the cause.

I have the same thing on mine all the time and I've noticed it on other boats. If your boat is running ok, I wouldn't lose any sleep over it. Just another job for magic erasers!!!

As far as the sucking sound, my 454 does the same thing, and after doing some research found it to be normal, air intake induction noise. almost sounds like a belt slipping on mine, but it's the air intake.

The soot probably only builds up when your idling, with your exhaust pipes where they are, theres no place for the exhaust to go except up and around the transom. So I would suspect the problem will never go away....unless

Is your exhaust switchable? Switching to through prop would probably reduce the soot buildup at idle.

We run into this big time in aviation with the soot coming off turbo-prop engines. We use a product called "Rejex" which is a type of wax we apply on all of our aircraft to help protect the plane from getting deep, hard to remove stains from this. I have waxed several of my boats over the years with this stuff stem to stern and do like it but it does not leave quite the shine that a good u/v resistant polish will so I only do the transoms now with the Rejex. Quite remarkable stuff, apply it at the beginning of the season and anytime I'm out floating on a mat around the boat I simply take my hand and splash/wipe lake water all over it and it just melts away.

Warning to all using Magic Erasers. They are abrasive and do scratch the shine off your gel coat leaving a more porous surface which allows for dirt and grime to build up quicker. Their abrasiveness is similar to a medium cut rubbing compound so the shine can be brought back after several rounds of lighter abrasive polishes. I am a huge believer in them and have used them on my boats interiors but only once as they scrub some of the vinyl off as well. If you can get it clean once, keep it clean and try not to continue their use. A good vinyl conditioner applied after their use and a wipe down after every outing should keep everything nice and clean so you won't have to use them again. But they are quite certainly a miracle.

I second the non use of them on the hull itself, they do work wonders on the rub rail though. I tried using them once on my car to remove some sticker glue after taking off the dealership stickers, it took the glue off as well as some of my clear coat. They can also damage plastic surfaces such as the dash.

How does Rejex work below the waterline?

I almost added a comment about the Rejex's performance against lake scum but didn't. Quite honestly it really didn't make a noticeable difference compared to other products I've used. Works wonders on the transom with respect to exhaust soot.

Bell Helicopters and the US Army contracted Corrosion-X to develop a wax type product that could be applied in particular to the flat paint used on military copters. Their Turbine Exhaust Trails were nearly impossible to remove and really stood out on Sand colored aircraft when everything changed from green back in the early 90's during Desert Storm. Eventually it became available to the civilian market and we use it exclusively on all aircraft we inventory and sell. I sell Pilatus and Piper which both offer single engine Turbo Props that leave their soot trails down the entire fuselage and is down right ugly. My line guys and literally hose it off without soap. Normal waxes still wouldn't put a secure enough barrier between the paint and the soot and it simply stuck and had to be scrubbed off.

Back to the waterline scum. I've tried pretty much every wax that's come out for boats, planes, cars etc. and have relegated myself to Yacht Brite Pro Polish as my twice a year "wax". It is UV stable and without question adheres the longest. I'm at Lake of the Ozarks which is not the cleanest of lakes and after every weekend I wipe down the boat with a synthetic chamois and always have a nice brown waterline. I apply it at the beginning and end of the season and do not notice a difference throughout the season as to the ease of removal of the scum line. It simply wipes right off with absolutely no scrubbing. Most every true wax I've tried seams to function like this for about 30 days then I'm re-applying to the lower portion to bring its effectiveness back. UV stability is key and most "polishes" are not. They also have a product called Buff Magic sold in a tin that is much like a jewelers’ rouge that is fantastic as a pre-treatment and incredible on stainless. Whenever I buy a new "used" boat I have a process. Assuming no fade or chalkiness I start with 3M Finesse-It Polish followed by Buff Magic and top coated with Pro Polish. From that point on it's easy to maintain.

Last year I started to experiment on my Malibu ski boat with some of the "spray detailers" to use between waxings. Once again I've gone thru about all of them and two stood out substantially. Turtle Wax Ice Spray Detailer can be applied in direct sunlight and was one of only two that actually removed hard water spots. My boat is red and white. The one that worked the best was Yacht Brite Serious Shine but it's in an aerosol can and very expensive. This weekend I'm going to try them both out on my Z302 and compare. My Mariah doesn't have what I would call a super glossy finish as most all other boats I've owned so I'm not sure it's really going to do anything. As far as I know it might strip off the polish...