Transom soot.

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John J

We have a new 310 with the 25xp engine. Everything runs well. As the summer has gone on the amount of exhaust build up on the transom is increasing. I wash it down after every time out. We generally run the engine about 1+ hours per outing. We do not leave it at idle excessively. Our dealer said it may be we are overloading the engine, but we have not run above 2500 rpm. Is there anything I should check? There does not appear to be any abnormal amount of exhaust while running.
 
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Gordon Torresen

Sooty transom

Your dealer is may be right, but overloading the engine does not relate only to RPM. If the boat bottom is extremely fouled, more HP is required and the overload can come on sooner. If the engine is not running properly, it does not develop full HP and thinks it is overloaded sooner. The problem could relate to the injectors. If one was dripping (not shutting off between squirts) excess fuel would be present the next time that cylinder was supposed to fire and it would not all be burned. If the injectors were not calibrated properly, one or more could be wanting the engine to turn faster than the other(s), hence exhaust with partially burned fuel. The Universal M25XP has more than enough HP for the Catalina 320 if all is in order. 2500 RPM sounds like a good cruising speed. If you have too much propeller you could be approaching over load sooner. I like to plot a graph of RPM vs hull speed, on a calm day. As RPM increases, so should boat speed, to a point. The graph usually makes a near straight line until the point where it requires extra RPM for a given increase in hull speed, ie: the line bends. The start of the bend is the most efficient speed to turn the engine. That speed should relate very closely to the theoretical hull speed. In the mean time, keep on scrubbing. That black stuff can do bad things to gel coat if left on too long.
 
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Mark Geigel

I have the same 310 exhaust problem

We are having the same problem with black sooty exhaust on our 310. We also run it for about 1 hour each time we use it and are also running at 2500 RPM or less. Somedays it's worse than others. 2 new boats with the same problem. Any ideas gang?
 
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Wally Boggus

Common denominators....

We all have new boats...new engines...operate at or less than cruising RPM's...and yet we have sooty transoms. So it would seem that the soot is either (1) normal or (2) there is something common among all that is wrong. I am starting to lean towards the possibility that it is to be expected, but wish there was something wrong with the engine that could be fixed as I'm tired of cleaning the transom after every outing. w
 
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John J

Sooty Transom

I am not a big beliver in coincidence in matters like this. Firestone said for years it was just coincidence! I think Gordon is right in that the problem lies in the injectors. It has reached the point I can wipe the transom with my hand and smell raw diesel. That combined with having to wash and wax it after every time out is ridiculous. I have made it very clear to my dealer that this is not acceptable. Allegedly he has scheduled a mechanic to look at it. When I know what he finds, I will post Has anyone called Catalina to pose this question? John
 
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Wally Boggus

Another mechanic...

I have a mechanic coming to check my valves and injectors next week also, so I will post his prognosis here. w
 
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John J

Transom Soot

Warren Pandy of Catalina has contacted me and said they are checking it out with Univesal to "see what they have to say or offer". I will post their response. My dealer is having someone come out, so as soon as I have something, I will post.
 
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Gary Groth

soot on transom

I have a 93, 36 Cat since new and have had the same soot on transom problem. The engine has been checked out several times and nothing is out of line. My question is, maybe the exhaust being in the water while motoring causes the fumes, which has diesel residue, to mix with the water and this then sticks to the tramsom. I noticed that other boat makers put the exhaust port higher on the side of the boat so it does not squat into the water while motoring and they do not have residue around their exhausts. I have talked to the Mainsheet Tech writer and asked about raising the exhaust, which is not a problem as long as you maintain the loop. I think this will solve the problem. I have never had black exhaust fumes visible, but I think its the nature of diesel exhaust to carry some residue and because it mixes into the water it ends up on the transom. Anyone ever notice there is no soot build-up after just idling at dockside.
 
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