[Fuzzdr]

Hello Folks; my wife asked me to inquire about a black superficial film that appears on the gelcoat finish after our Cummins 8.3 engines have been running for awhile. It is absolutely superficial and has not penetrated the surface at all. She is a cleaner and this does bother her. The boat is of the 1997 vintage. Could the engines somehow be out of adjustment causing the diesel fuel mixture to be too rich? Incomplete combustion? What else could be wrong? Or is this normal and to be expected in an older boat?

More importantly what can we do to eliminate or reduce this problem? Any fuel additives that would help?

Any assistance will be greatly appreciated.    Fuzzdr

[ReelMagic]

I have a 2003 38 Open w/Cummins 6CTA's and get a small black film near the exhausts after running long periods..... Easily removed but was told to remove/clear the AFTERCOOLERS.. Did just that and problem disappeared... Not sure if you have done that or not but would recommend doing it.....Solved my problem.... Will do again this coming winter as there were last done in 2011.... Have about 600 hrs on them since they were done.... M2C

[Fuzzdr]

Thanks for your note ReelMagic. Interesting- no I have not removed and cleared my Aftercoolers. Not even sure how I would do that? I have only had this 1997 Tiara 4000 Express for 3 weeks now. I do have lots to learn as it is very different and larger than my last boat. But the learning process is fun! Fuzzdr

[ReelMagic]

There is a web site that describes how to remove/clean aftercoolers on Cummins 6 CTA'a.. use link: [Only registered and activated users can see links Click here to register]

[jclark003]

Some soot is normal. Is it happening more on one side? How many hours on boat? Salt or fresh?

After coolers if plugged on the air side can cause your engines to soot. You should check your engines maintenance schedule and past history to determine if a cleaning is in order. before heading down that route I would first inspect the air cleaner as if that is restricting airflow you will most certainly soot up the transom. Other culprits include fuel pressure (sucking air through a fitting, Racor or secondary filter), bad injector or warn turbine/hot housing off the turbo which may be accompanied by somewhat poor mid range acceleration.

[Sans Peur]

If you are new to Diesels I would heavily suggest getting on [Only registered and activated users can see links Click here to register] and getting a subscription. It's pretty cheap and the people on there know friggin everything about these engines. I have been on it for quite a few years now and it is invaluable.

To your problem, the advise above is good. However, those older engines will produce soot. Sometimes it is just something you have to put up with. I have a pair of Cats and the transom gets a little on it from time to time, especially if I am running hard in some rough water. Does your boat run up to max rpm? If you are over propped or the bottom is fouled the engines could be working harder and will produce more soot as well.