Cat 3116 Soot

[Pierpressure1]

I figured it would be better to start a new thread since Keith has a different motor than I do.

Just got back from a week long cruise and had soot on transom after each stop. It was worse when I had in big seas and was unable to cruise above 2200 rpms.

I just installed digital Tachs and confirmed the boat is only able to reach just under 2700 rpms with each engine. This was after diver cleaned hull and running gear. Last year when I launched it did hit 2800 but we have much more gear stowed onboard and the old tachs May have been off.

I know dirty filters could cause soot but boat is either having engine power issues or is over propped. There are no Cat mechanics in my area so I figured best approach would be to repitch the props by 1” and clean the filters.

Does this sound like a sound approach?

In the past year I have pulled the aftercoolers and had them pressure tested and cleaned by radiator shop. All fuel filters are new and I am following Frank’s recommendations on fuel additive. The bottom paint is new but there are multiple layers with some flaking that I plan to have blasted off this offseason.

Adam

 

[fwebster]

I just went thru sand blasting 20+ years of bottom paint accumulation off the bottom of my boat. My history is to haul out every year for a few days in February, check the bottom condition, touch up the waterline and any other spots that need it, then do a full bottom job every 3 years...heavy sanding was the repaint prep. I had no bottom issues like blistering but the boat was 20 years old and the bottom was pristine so we barrier coated with an epoxy barrier coating then painted as usual with bottom paint.

I couldn't believe the difference in performance. Getting rid of the old bottom paint weight and surface imperfections and we picked up between 2-3 kts and about 100 rpm @ WOT. Sooting was decreased because the engines had been slightly overloaded at cruise, but I knew that and never ran over 2300 rpm.

At the same time.......20 years and 1400 hours on both engines.......we had the after coolers removed and cleaned. Now, the only sooting we get is just around the exhaust outlets on the side of the hull.

Now, you are on the right track: Your engine are overloaded and the causes soot. But don't try to tell the prop guy what to do. He is the professional so just tell him that your engines need to turn up 100 more rpm on each side then let him do what he thinks he needs to to get you the 100 rpm you need. Most reputable prop shops will then tweak the props as needed after you get them back on the boat and run it with a clean bottom and normal loading and see your WOT rpm. Besides shifting the responsibility of tweaking to the prop shop, he might be able to get you what you need in a simpler easier way without affecting speeds like just removing a little but of cup. The other thing is that in a 20-24" prop, 1" of pitch is equal to 3-400 rpm, way more then you need.

Another cause of sooting is restricted intake air. Are your air filters clean? What oil are you using? If you don't know prior to your buying the boat or if the engines have been running multi-viscosity oil, your boat is 20 years old now so you may want to have the after coolers removed and cleaned to clear any fouling on the air side. That is also a great time to replace the engine hoses that are nearly impossible to get to under the aftercooler cover with the after cooler in-place. It is also a good time to replace your engine coolant since it all must be drained to remove the after coolers.

As you work thru this, keep in mind that 3116's have unit fuel injection and while they are inherently clean starting, clean burning smoke free engines, they are still mechanical diesels so there is going to be some minor sooting even if you get all the other possible causes checked and handled.

 

[Pierpressure1]

I just went thru sand blasting 20+ years of bottom paint accumulation off the bottom of my boat. My history is to haul out every year for a few days in February, check the bottom condition, touch up the waterline and any other spots that need it, then do a full bottom job every 3 years...heavy sanding was the repaint prep. I had no bottom issues like blistering but the boat was 20 years old and the bottom was pristine so we barrier coated with an epoxy barrier coating then painted as usual with bottom paint.

I couldn't believe the difference in performance. Getting rid of the old bottom paint weight and surface imperfections and we picked up between 2-3 kts and about 100 rpm @ WOT. Sooting was decreased because the engines had been slightly overloaded at cruise, but I knew that and never ran over 2300 rpm.

At the same time.......20 years and 1400 hours on both engines.......we had the after coolers removed and cleaned. Now, the only sooting we get is just around the exhaust outlets on the side of the hull.

Now, you are on the right track: Your engine are overloaded and the causes soot. But don't try to tell the prop guy what to do. He is the professional so just tell him that your engines need to turn up 100 more rpm on each side then let him do what he thinks he needs to to get you the 100 rpm you need. Most reputable prop shops will then tweak the props as needed after you get them back on the boat and run it with a clean bottom and normal loading and see your WOT rpm. Besides shifting the responsibility of tweaking to the prop shop, he might be able to get you what you need in a simpler easier way without affecting speeds like just removing a little but of cup. The other thing is that in a 20-24" prop, 1" of pitch is equal to 3-400 rpm, way more then you need.

Another cause of sooting is restricted intake air. Are your air filters clean? What oil are you using? If you don't know prior to your buying the boat or if the engines have been running multi-viscosity oil, your boat is 20 years old now so you may want to have the after coolers removed and cleaned to clear any fouling on the air side. That is also a great time to replace the engine hoses that are nearly impossible to get to under the aftercooler cover with the after cooler in-place. It is also a good time to replace your engine coolant since it all must be drained to remove the after coolers.

As you work thru this, keep in mind that 3116's have unit fuel injection and while they are inherently clean starting, clean burning smoke free engines, they are still mechanical diesels so there is going to be some minor sooting even if you get all the other possible causes checked and handled.

Frank

Thank you for the quick response. I have pulled the aftercoolers to have the professionally tested and cleaned and took that opportunity to replace the hoses and clamps. The previous owner used the cat 30 weight oil and I have used Rotella t1 30 weight.

I will clean the air filters as it has been about a year since last done and take your advice on the prop adjustment. Your experience with the bottom job has me convinced it is time to tackle it this offseason.

Is there an issue with turning too many rpms if the prop is tuned this summer to increase wot and the paint is removed later which may provide additional rpms as you experienced?

 

[fwebster]

Frank

Thank you for the quick response. I have pulled the aftercoolers to have the professionally tested and cleaned and took that opportunity to replace the hoses and clamps. The previous owner used the cat 30 weight oil and I have used Rotella t1 30 weight.

I will clean the air filters as it has been about a year since last done and take your advice on the prop adjustment. Your experience with the bottom job has me convinced it is time to tackle it this offseason.

Is there an issue with turning too many rpms if the prop is tuned this summer to increase wot and the paint is removed later which may provide additional rpms as you experienced?

Too many rpm's?......but that is a situation we almost never see. I wouldn't think so as long as you don't run over 2800 rpm more than 8% of the time and keep cruise speeds below 2400 rpm which are within the designed parameters. Typically boats slow down some as the season wears on so it is actually better to have the boat turn a bit over 2800 with a fresh bottom because it is going to slow down a bit as the season progresses.

 

[Pierpressure1]

That makes sense. Thanks again for your help.

Adam