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...

Lots of good information thanks for the reply Milemarker60!!!

That's extremely interesting reading Dave, thanks for the information. Mequires seems to be the preferred product for most of the guys here, so these top of the line alternatives could certainly save some from a lot of hassles and heartache. I may even give that Turtle wax a go to get rid of some of my hard water spots I have accumulated.

Thankyou.

I use Super Strength, from the Dollar store. Belive it or not, it is VERY strong. I use it on all of our construction equipment to get the grease off of them. Be careful, if you let it sit on there in the sun, or dry it stains the surface. Have you looked into painting your boat? Our's is painted on the bottom because it use to sit in the water (now its in a lift) and it doesn't look beautiful going down the road but, it looks good when you pull it out!!:) Just a thought! Painting isn't cheap though. $2600 dollars (US)

mis4tun81, I do have silent choice but a small amount of exhaust does come out of the pipes at idle. I think due to back pressure of forcing down lower unit when not on plane.
I use 3M boat wax and it seems to work well, the soot wipes right off. My brother uses ICE and likes it, but he says it needs to be applied more often than other waxes or polishes he has used.
I have another related question.:confused: There is only two gas stations left in town that has gas without ETOH. One, Shell 87oct @ 4.19/gal and one truck stop with 91oct @ 4.18/gal. I know you shouldn’t run lower octane than a engine is rated for. But, I should have no problem running the higher octane in my 87oct rated engine all the time, Right? I would think it will give my more power and maybe burn cleaner.
Thanks for all the info!

You are absolutely right, running a higher octane in any engine (marine or road) will give you better economy, cleaner burning, longer engine life, and most important more power!
My cars handbook says - Vehicles with engine management systems will automatically adjust the motor to suit the octane rating of the fuel being used - dont ask me how it knows though!

Late model cars use a combination of knock sensors, oxygen sensors, air mass meter and various temp sensors to determine the proper fuel mixture and timing. The computer then adjusts the injector flow and ignition 'dwell angle' to the optimal settings for the fuel you are using as well other variables, i.e. humidity, intake temp, contamination of oil by fuel, etc.

The really neat thing is that the computer via the knock sensors is able to determine which cylinder is beginning to knock and adjust the timing on that individual cylinder. It is possible for the computer to set individual timing on every cylinder at the same time.

As far as boats are concerned, since the pollution controls are not required, my guess is that they use a much less sophisticated approach. :)

Graydog you posted as I was typing and thinking this out.:D

Hmmmm,

If this were a car or motorcycle forum I would disagree with you (dudders), ;)

which is why I waited a little to think about my response.

Cars know what the fuel octane is by using a knock sensor which listens to the knock or pinging in an engine and tunes accordingly. Most newer injected boat engines have a knock sensor as well.

However, normally aspirated non performance car engines are tuned to run best (within EPA limits) using the recommended fuel.

This is true, however most knock sensor & ECU's detune the car if a lower octane, or bad gas is put in the tank that increases knock, the ECU detunes the car by retarding the timing from optimum to eliminate the knock. Not generally the opposite.

Higher octane fuels reduce pinging by being harder to ignite, they contain similar amounts of energy, however it is harder to release that energy. Higher compression engines take advantage of that and are tuned more aggressively, without the fuel preigniting. They get more power by using more fuel in an engine that is built to use it, not the higher octane.

OK HERES WHY BOATS MAY BE DIFFERENT

Engines are more prone to preignition (pinging) under high loads at full throttle, especially at low RPM. Not as common in a car (unless you drive like I do:eek_animated:) but very common in a boat (especially if you drive like I so :D)

So with a lower octane fuel in these conditions, your engine MAY retard timing slightly at full throttle, if it does, a higher octane fuel might reduce this tendency.


Practically speaking,

I am chasing a low top speed/RPM (4200) in my 2001 454 MPI Z275 that I don't suspect is the prop selection, because it is original equipment.

So far I have only tried two things to improve it, one I cleaned my air intake/spark arrestor, and at the same time, put some injector cleaner in the tank, and decided to run higher 91 octane fuel to see if things would change.

They did, I lost another 200 RPM and 4 MPH.

Last night I pulled the distributor cap and the terminals are pretty corroded worn, so I will do a tune up, plugs, cap, rotor, maybe wires. And see if anything change.

But in my opinion and experience as with cars, you may not see an improvement by running a higher octane fuel.

The tune up will certainly not harm you, but I would wait until you have run enough fuel through the system to insure your performance is not being skewed by the fuel injector cleaner.

How long has it been since you changed your oil, contamination from a previously rich mixture can really screw up how your engine management system regulates itself.

Also, make sure your trim is working correctly and you don't have any drag on your hull (read "crap"). My experience is that performance problems are more often than not cumulative and not just based on one major problem.

What's the old saying, "The devil is in the details."

And when all else fails, check to make sure that you pulled your anchor before trying to reach top speed. :D

Thanks for the feedback,

Oil has 20 hrs on it and is clean, I suppose the injector cleaner could be tweaking the tune a little, I put a mild mix, compared to what I would do to a car or bike since it will be in there for a while. So I would not expect to notice a difference.

Boats clean, trim does what its supposed to do.

I will be putting the tune up parts in this weekend, the boat had 200 hours on it, and it looks like the cap rotor and wires at least are probably original, so as you said wont hurt.

The boat is new to me, so before I do something drastic I figured I would go over all the devils details, before I accept it or prop it.

Once I do the tune up I will know where I stand.

Thanks

Thanks for the replies guys, I stand corrected and will pass this info on to my mechanic who furnished this info to me in the first place. He owes me a beer now. Great.
Good luck getting your motor sorted missfortunateone. Happy boating over your summer period. Hope the floods we are hearing about arent affecting any of you guys.

My Z210 with Captain's Call shows soot on the transom around the oval exhaust ports after each trip. Like yours, it's not heavy soot, but enough that I wash it off when returning to port (which is my garage). Like the rest of you, I wax hard once per season and the soot washes off pretty easily.

Regards,

Adjusted Choke
 

on our 7.4 weber carb, we adjusted the choke and it barely smokes at all. I don't hear much of a hissing noise, but thing runs much more smoothly after correcting the choke.