CAT 3116 Transom Soot

[Avalon36]

I have a freshly rebuilt 3116 in Avalon, now with 100 hours on it. Engine runs great but it is still sooting up the transom. I get 2750 rpm @ WOT (Spec is 2800)and get 15 knots +/- depending on sea state, which for a 22K displacement Downeast, is not bad. Prop has been recently pitched (currently 23x16), with a 1.5:1 reduction turning a 1.75" shaft. The guy who did the rebuild is 5 hours away so is not available to look at the engine. Engine is not burning oil. Engine temp is right at 185* with a laser gun. My local factory certified CAT mechanic is suggesting that he start from the beginning and re-calibrate/rerun the injection rail as he thinks it may be running rich. That may not be a bad idea but I have gotten some more than questionable advice from him on several engine related issues so I am just a bit suspect and don;t want to spend $1K for nothing. The boat is on the hard for the winter but March will be here before we now it! Any thoughts and/or suggestions will be most appreciated.
Cheers & Happy Holidays!

 

[O C Diver]

What does the rebuilder say?
While you won't be able to do it till spring, pictures are extremely helpful. Clean the transom and run it for a day. Maybe periodically stop, take a couple of pictures, note time, cruising speed and RPM. One person's sooted transom, maybe normal or near normal based on hours since rebuild. Hard to define the level of soot without pictures.

Ted

 

[sunchaser]

Avalon
You say "still sooting up the transom". I assume this means it was doing this before the engine work? Why did the engine fail?

It may well be propped wrong. Three recommendations before spending time on the engine beyond the easy and obvious:

• Get a photo tach and verify RPMs at several points
• Assuming you have the 325 or 350 HP version, you should be pulling 2850 or so WOT under load with boat fully loaded and clean bottom
• Do prop work to get RPMs up as verified by photo tach

 

[Ski in NC]

2750 at WOT is not enough. You want about 2850. Also, what rpm/speed do you cruise?

Always good to go back through the rack and top set after a rebuild and 100hrs to compensate for any changes in settings from break in.

 

[Avalon36]

Thanks for the feedback gents!
The boat is new to us and we just completed a hull up refit. Every system is new including the 300 HP "E" version 3116. The CAT Spec is 2800 RPM at WOT, which we have achieved with a photo tach. The analogue tach(s) both show 2750 (+ish) which the CAT tech says is fine.He doesn't think there should be any soot, hence the suggestion to run the rail. We normally cruise at 1900-2000 rpm. Prop shop and Michigan Wheel both agree that pitch is correct after we took 2" out earlier this year. Running the rail is certainly not out of the question and probably good idea. Just don't want to spend the $$$ on that if there is something else that is the actual root cause.

 

[High Wire]

Cat 3116s need straight 30 or 40 weight oil per a engine bulletin years ago. Is that what you run? My friends 3116/T300 hp boat will soot a little after 4-10 hours running. He is under-propped.


Of course the link no longer works.
https://parts.cat.com/wcs-static/pdfs/PEWJ0074-04.pdf


Here is part of it:
Engine Oil (3116 and 3126
Marine Engines)
SMCS Code:
1348; 7581
Recommendations
Cat does not recommend the use of multigrade oils
in the 3116 and 3126 Marine Diesel Engines that use
mechanical unit injection (MUI).
Multigrade oils use high molecular weight polymers
as viscosity index improvers. When the crankcase
blowby flows through the turbocharger and the
aftercooler, the viscosity index improvers can adhere
to the turbocharger compressor and aftercooler core.
The fouling of the turbocharger and aftercooler can
cause reduced air flow, loss of power, and increased
black smoke. The emission of black smoke results in
buildup of soot on the transom of the boat.
Note:
Cat recommends the use of single grade oils
that pass all API CF-4 category requirements unless
crankcase blowby has been routed away from the
air cleaner inlet.
Cat SAEO (Special Application Engine Oil)
Note:
Cat SAEO is recommended for use in Cat 3116
and 3126 Marine Diesel Engines with mechanical
unit injection. 3116 and 3126 Marine Diesel Engines
that begin with the following serial number prefixes
are included: (S/N: 6SR), (S/N: 8NM), (S/N: 4KG),
(S/N: 1SK), (S/N: 1ZJ), (S/N: 6MK), and (S/N: 4EZ).
The factory-fill for 3116 and 3126 Marine Engines is
Cat SAEO with the following properties:
•
Meets all requirements of API CF-4 category
•
Viscosity grade of SAE 30
For maximum performance in 3116 and 3126 Marine
Diesel Engines with mechanical unit injection, Cat
recommends the following engine oil:
•
Cat SAEO (SAE 30)
•
Cat SAEO (SAE 40)


Commercial Oils (3116 and 3126
Marine Engines)
NOTICE
Cat does not warrant the quality or performance of
non-Cat fluids.
When Cat SAEO is not used, use the following
commercial oils:
•
Single grade oil with a viscosity of SAE 30 or SAE
40 that meets all API CF category requirements
is preferred.
•
Single grade oil with a viscosity of SAE 30 or
SAE40 with an API CF additive package and no
viscosity improvers is acceptable oil.

 

[Avalon36]

Thanks for all the great info, Archie. Really helpful. The guy who rebuilt the engine recommended using 15w/40 which is clearly counter to what CAT is recommending. Come Spring time, I will change the oil again and go with straight 30 weight oil.

 

[hmason]

Thanks for all the great info, Archie. Really helpful. The guy who rebuilt the engine recommended using 15w/40 which is clearly counter to what CAT is recommending. Come Spring time, I will change the oil again and go with straight 30 weight oil.

I have twin 3116s. I only use CAT SAEO 30 weight oil and have no soot on transom. The label on the jug reads: Special Application Engine Oil for the 3116 and 3126 marine engine. It is available at CAT dealers. Check prices. One distributor quoted $38/gallon and the one I bought it from charged me $22/gallon.

 

[Delfin]

Thanks for all the great info, Archie. Really helpful. The guy who rebuilt the engine recommended using 15w/40 which is clearly counter to what CAT is recommending. Come Spring time, I will change the oil again and go with straight 30 weight oil.

Not sure I would wait. There have been some issues with the 3116 that the oil of supposed to address.

 

[Bigsfish]

One of my boats I kept for 21 years had twin 3116 (300 hp). A friend who helped develop the 3116 for Cat always told me they were designed for 300 hp and I never had a problem other than aftermarket exhaust which was fixed. I always use the Cat fixed weight oil. They smoked very little but only when towing a 25 ft open fishermen.

 

[Avalon36]

Not sure I would wait. There have been some issues with the 3116 that the oil of supposed to address.

Good advice but the boat is on the hard and the engine has been winterized so the oil change will have to wait until she splashes again in March.

 

[Avalon36]

One of my boats I kept for 21 years had twin 3116 (300 hp). A friend who helped develop the 3116 for Cat always told me they were designed for 300 hp and I never had a problem other than aftermarket exhaust which was fixed. I always use the Cat fixed weight oil. They smoked very little but only when towing a 25 ft open fishermen.

Thanks for the feedback! Will go with the CAT 30W and see what happens.
Cheers!

 

[twistedtree]

When a tech talks about a diesel "running rich", it's time to run away.


As others have suggested, the sooting may be normal. It's real hard to tell.


I assume you have checked the air filter? And the turbo (if it has one) is producing the requisite boost pressure? Do you have any accurate way to measure fuel burn? It should be according to spec at WOT. If more, then definitely over loaded.

 

[bayview]

15 Knots may not be fully on plane and 2750 is low. Are you using trim tabs? Is that the makers weight or actual scale weight? Were the injectors rebuilt with the engine? consider measuring boost and do check the air filter and run with the ER hatch open as a test to see if there is any restriction. Look for boost air leaks at post turbo hose tubing connections.

Is the bottom and prop really clean now?

 

[sunchaser]

I have a freshly rebuilt 3116 in Avalon, now with 100 hours on it. Cheers & Happy Holidays!

Where was the engine rebuilt and what was done? A factory CAT reman is one thing, a Cat trained mechanic working out of an independent shop another. With wrong oil recommended what else may raise a red flag from the re-builder and your mechanic? Be suspicious.

Since no meaningful work can be done on vessel until re-splash time suggest that with engine, fuel pump and injector numbers in hand you compare what you have to what Cat says should be there. Dave on boatdiesel is a good source for this sleuthing.

Do not reject that you may be over propped. Until a fully loaded 2850 can be achieved, a question remains.

 

[Cigatoo]

Where was the engine rebuilt and what was done? A factory CAT reman is one thing, a Cat trained mechanic working out of an independent shop another. With wrong oil recommended what else may raise a red flag from the re-builder and your mechanic? Be suspicious.

Since no meaningful work can be done on vessel until re-splash time suggest that with engine, fuel pump and injector numbers in hand you compare what you have to what Cat says should be there. Dave on boatdiesel is a good source for this sleuthing.

Do not reject that you may be over propped. Until a fully loaded 2850 can be achieved, a question remains.

2900 would be better. Verified with photo tachometer. However before checking loaded RPM check that no load W.O.T. RPM (Neutral) is obtainable based on cat specs for your engine. Again with photo tachometer.

Worthwhile getting the correct Cat manual for your engine so you are not relying on the internet for correct info.

I can tell you that being 100 RPM over propped will leave soot on your transom while exhaust appears to be clean (no smoke).

Your Cat will love being 100 RPM under propped

 

[Avalon36]

Thanks again for all the feedback and support. I'll try to address several questions that have been asked.
This is a Royal Lowell designed downeast hull with round chines. She gets up on a fairly good plane but the folks who did the layup (Nausett) said that with this power plant, the cruising sweet spot should be right around 2000 rpm with an SOG of 9-10 knots, which what we are getting. There isn't much bow rise and the Nausett has recommended not using trim tabs.
We put 105 hours on the engine, burning 450 gallons for an average of 4.5 GPH. ~75% of that time was at 2000 rpm.
The weight (22000) is spec and also the fully loaded weight per the travel lift at launch. Injectors were rebuilt, as far as I know. Air filter (Walker Air Sep) is new.
WOT with no load is 3200 and 2750(+/-) under load with the ER hatch open or closed per a photo tach. I initially achieved 2800 with a freshly cleaned bottom but lost 50 rpm (+/-) after the boat was in the water a couple of weeks. Checking the boost is certainly worth doing.
The 23" prop was originally pitched at 18" and was re-pitched to 16" because I was only getting to 2400 RPM at WOT, which wasn't actually WOT because the throttle linkage was attached to the wrong point on the throttle lever (Really?). Corrected that and immediately achieved 2800 with the prop pitched at 16" (think we got very lucky on that adjustment).
The CAT mechanic has suggested pulling the after cooler to see if there is any carbon build up on the valves and/or turbo and re-running the rail, both of which are not bad ideas but something I would prefer not to do if they are not really necessary.
I will certainly change the oil with CAT SAEO 30 weight in the spring.
Question for everyone: The CAT Spec is 2800 RPM @ WOT so why are so many responses commenting that 2750 is low d that I should be getting 2850 or 2900?

 

[BIG CAT]

"Running rich". That's a first.

 

[Avalon36]

"Running rich". That's a first.

I suspect he may have been dumbing things down for my perceived benefit. If the turbo pressure is low, would that not result in the equivalent of running rich?

 

[BIG CAT]

I suspect he may have been dumbing things down for my perceived benefit. If the turbo pressure is low, would that not result in the equivalent of running rich?

Black smoke is most commonly poor air/fuel ratio. Several things can cause it. Low boost is one. Some Injection pumps have a a/f ratio control that can cause problems as well as a restricted after cooler or filter.



I would fallow the advice above. The 3116/3126 have a specific oil made for them.

 

[Avalon36]

Black smoke is most commonly poor air/fuel ratio. Several things can cause it. Low boost is one. Some Injection pumps have a a/f ratio control that can cause problems as well as a restricted after cooler or filter.



I would fallow the advice above. The 3116/3126

have a specific oil made for them.

Will do. Just to be clear, there is no visible smoke in the exhaust, just soot appearing on the transom.
Thanks!

 

[Cigatoo]

“I initially achieved 2800 with a freshly cleaned bottom but lost 50 rpm (+/-) after the boat was in the water a couple of weeks.”

Dumb question but how much weight did you add in those couple of weeks? Cruising comforts get heavy. Did you shift any weight forward or aft? How about fuel? Did you fill the tanks? Did you pick up some trap warp on the running gear?

Low boost could certainly be a cause. You also might want to consider adding an exhaust gas temp gauge. They tell a story.

Good luck.

 

[Avalon36]

“I initially achieved 2800 with a freshly cleaned bottom but lost 50 rpm (+/-) after the boat was in the water a couple of weeks.”

Dumb question but how much weight did you add in those couple of weeks? Cruising comforts get heavy. Did you shift any weight forward or aft? How about fuel? Did you fill the tanks? Did you pick up some trap warp on the running gear?

Low boost could certainly be a cause. You also might want to consider adding an exhaust gas temp gauge. They tell a story.

Good luck.

All good questions but the answer is very little, if any. Fuel and water tanks were filled at launch and we had all the major "stuff" on board. Bottom and running gear has stayed relatively clean with use, a short haul and a diver. Will check boost. What does an exhaust temp gauge tell you? What should the temp be?

 

[Cigatoo]

EGT is a direct indicator of load on the engine. Higher temps equal more load. Cat specs should tell you where to insert the probe (before ot after turbo) and what max temp should be. You can also get combination EGT / Turbo boost gauges.

https://www.sbmar.com/product/smx-marine-boost-pyro-turbocator-gauge-kit/

Will not solve your current problem but will give you insight and a baseline.

 

[Avalon36]

Thanks for the follow up and link. Very, very helpful!

 

[twistedtree]

What does "re-running the rail" mean?

 

[Archhibb]

Question for everyone: The CAT Spec is 2800 RPM @ WOT so why are so many responses commenting that 2750 is low d that I should be getting 2850 or 2900?

When it comes to marine diesels, overpropping is black & white; either you are or you’re not, and even a little is very bad for engine longevity. Cat specs 2800, but they base that on the best case scenario and just assume you’ll follow it to the letter. And if you don’t, they’re happy to sell you a new engine...

Putting two and two together, I realize you posted earlier on the downeast forum. It’s a safe bet that your custom Nauset cruiser is made from the Royal Lowell 35ft. sport cruiser mold that Nauset acquired when Bruno Stillman went out of business. They made a number of 35’s but if I’m correct, yours @ 22,000# might be the heaviest I’ve heard of.

That is a lot of boat for 300hp. For comparison, my 15,000# Five Islands 35 (same Royal Lowell hull design) with the same 300hp 3116 gets 11 kts @ 2000.

Getting the fuel rail and injectors synchronized is a good idea. But if you want to truly know if you’re overpropped or not, spend less money and have a pyrometer installed. The EGT’s will tell you whether the engine is operating within acceptable load tolerance.

 

[Delfin]

When it comes to marine diesels, overpropping is black & white; either you are or you’re not, and even a little is very bad for engine longevity. Cat specs 2800, but they base that on the best case scenario and just assume you’ll follow it to the letter. And if you don’t, they’re happy to sell you a new engine...

Not so sure that this is correct. A vessel can be overpropped a bit and as long as you're not running around at WOT I'm not sure you'll see any disadvantage. Having the new CAT in Delfin run up by CAT for warranty certification, she made the 2200 rpms specified. But at that point, she was an empty shell and 10 tons of stuff later was overpropped and could only make 2050. However, at 7 knots or so, I need only about 50 hp of the 270 available. With the overpropping, EGT was around 300 degrees, so I'd be hard pressed to think she was being over loaded, or am I missing something?

 

[Archhibb]

Perhaps, but all the reading I’ve done on BoatDiesel indicates that overpropping is overloading the engine throughout the entire powerband, not just at upper rpms. I’m not a diesel expert, but for a mechanical engine like the 3116, the throttle position equates to a given amount of fuel, but the overloaded engine isn’t able to develop the proper rpms. Now the fuel/air ratio is incorrect. Any overloading can lead to excessive heat and wear, and the Cat 3116 is known to be sensitive to overloading. Read up on the #6 exhaust valve.

Just my $0.02 and welcome other opinions.

 

[Delfin]

Perhaps, but all the reading I’ve done on BoatDiesel indicates that overpropping is overloading the engine throughout the entire powerband, not just at upper rpms. I’m not a diesel expert, but for a mechanical engine like the 3116, the throttle position equates to a given amount of fuel, but the overloaded engine isn’t able to develop the proper rpms. Now the fuel/air ratio is incorrect. Any overloading can lead to excessive heat and wear, and the Cat 3116 is known to be sensitive to overloading. Read up on the #6 exhaust valve.

Just my $0.02 and welcome other opinions.

There are those who would argue that slight over propping on a trawler putting along at low rpms is beneficial because it puts a higher load on the engine and helps prevent glazing. Dunno whether that is true or not.

P.s. diesels don't consume a set quantity of fuel based on throttle position, but on load. More load, more fuel.