Is our 28TE/Cummins 250 overpropped?

[Nancy]

I posted this on boatdiesel.com a few days ago and would like to get input from the folks here.

In April, we took ownership of our 1995 Albin 28TE. The engine is a 6BTA5.9 M1 250 HP engine with just under 700 hours. We´re new to diesels, so this is a bit of a learning curve.

We´re getting black smoke at certain RPMs, and we´re not getting rated/WOT RPMs (2600) let alone the 100-200 over that Tony Athens talks about repeatedly.

The fuel tank was nearly full when we took delivery. The previous owner said the fuel was fresh last fall. We ran through about half a tank and then refilled. The tank is now about half full again.

Here´s a rundown of what we´re seeing with a warm engine:

975 rpm at hull speed
1500 rpm+/-: smoke begins to darken
1900 rpm: more black smoke
2200 rpm: less black smoke
2440 rpm: minimal black smoke
2560 rpm: WOT under load; white mist/steam

1900-2000 rpm: most black smoke

3100+ high idle, no smoke

These RPMs were recorded using a tach tester, which gave readings about 25 RPMs less than the gauge.

Air filter is new.
Turbo inspected, seems good.
Plenty of engine room ventilation.
No loose or broken hoses on intake or exhaust.

Except for the black smoke, engine runs well and sounds good.

We have not dismantled the aftercooler or the exhaust elbow.

We've added Stanadyne to the fuel. Black smoke might have decreased very slightly, but not dramatically.

Based on many readings of Tony´s articles, we´re leaning toward overpropping as the problem. The prop is Nibral 4-blade 18x21. Transmission ratio is 1.4.

We´re in fresh water if that makes a difference.

Would welcome your input.

[jleonard]

Black smoke is bad. That means the engine is retaining heat, as in high EGT that is bad. Sounds to me that you are over propped. That will shorten the engnine's life as you have read in boatdiesel.
The 3100 at high idle is a little high I think. 3000 sounds like the spec but this is from memory.
You need to get at least 100 rpm over the rated 2600 at WOT.
You will gain efficiency and might even gain speed.
Those 250 hp engines are marginally cooled and they need to be loaded like a 220 hp engine to last.

[Nancy]

Time for an update.

We used the boat last summer, staying away from any range which produced black smoke.

In the fall, we took the prop to H&H Propeller in Boston, and they modified it from 18x21, #5 cup, to 18x20, #3 cup.

The results are in, and they are preliminary, but good. The boat reached a hair over 2800 rpm today with only a faint amount of black smoke getting over the hump around 2100. Maximum speed at WOT was 23.3 knots.

We'll be taking more readings, but we're pleased so far.

[jleonard]

Great. Your engine will be much happier

[Russell]

That sounds real good to me. Add a couple of passengers or weekend supplies and you will still be able to make 2600 RPM.

[Nancy]

That sounds real good to me. Add a couple of passengers or weekend supplies and you will still be able to make 2600 RPM.

I had one passenger aboard, and only one case of beer. Yes, I think it will be fine.

[RobS]

I had one passenger aboard, and only one case of beer. Yes, I think it will be fine.

Ah, the one to one ratio, very nice. Oh, and great job on the propeller loading adjustment

[captvz]

Hi Nancy,
I also have a 28TE (1994) with the same 250 hp Cummins diesel. I got the boat at the beginning of the season last year and it had 147 total engine hours. I was also having a smoke problem but was burning older fuel. After running the boat for a month I replaced the fuel, put in an additives to stabilize fuel and installed a new air filter. The smoking was much better and if not completely resolved this year, I will review the prop size and adjust accordingly. I am in fresh water and the boat has always been in fresh water. I appreciate your input and look forward to future contact.

I am still curious about whether there is a need to supplement the fuel with additives since the engine was made before the low sulfur fuel arrived. Would appreciate any suggestions.

Thank you,

Captvz

[jleonard]

All diesels smoke. Esp when cold. How much is a relative thing, some will always smoke more than others. When it gets excessive, then there might be an issue depending on what color the smoke is.
You don't need any additives. Sulfur is dirt and low sulfur fuel is better. It has all the lubricity the injection pump needs.

[eseyoung]

NO you are incorrect, Sulfur isn't 'dirt' and low sulfur is only better for the emission components, much worse for injectors and pumps.

Sulfur helps provide lubrication to injectors and injection pumps. as a matter of debate how much lubricity does an engine need? i can't speak to my boat or any others but what i do know is that my truck (Duramax) HATES IT. when we transitioned from LSD to ULSD i could definably hear more knocking, tapping and noise when i got a tank of ULSD. Now that ULSD is exclusively available i run a pint of two stroke oil in every-other tank. The ear feel of the engine is pretty close to what it was before ULSD. By the end of the second tank i am getting a slight surge and increased injector noise.

good read that backs up what i hear...

http://www.dieselplace.com/forum/76-gm- ... sults.html


From the website "ULSD fuel is the fuel currently mandated for use in all on road diesel engines. This fuel burns cleaner and is less polluting than it’s predecessor, called Low Sulfer Diesel Fuel. Low sulfer fuel contained less than 500 ppm of sulfer. ULSD contains 15 ppm or less.
As diesel fuel is further refined to remove the polluting sulfer, it is inadvertently stripped of its lubricating properties. This vital lubrication is a necessary component of the diesel fuel as it prevents wear in the fuel delivery system. Specifically, it lubricates pumps, high pressure pumps and injectors."

[jleonard]

Well I guess one man's dirt is another man's lubrication. You can have my share of sulfur in your fuel, I'll take mine lean.
My Dodge/Cummins truck didn't seem to care what it burned for fuel. Neither did the marine Cummins.
USLD has much more lube in it than LSD had. They corrected the issues that LSD caused. At least that what I have read.
Your "knocking" may have been caused by a slight difference in timing because of the different fuel mix or cetane level, etc. If lack of lubrication caused an audible knocking or clanking the pump would have self destructed from the metal to metal contact. One place I worked we made diesel fuel valves and the tolerances were so tight any deformity or galling would have locked them up.

[RobS]

I go by what I read over on BD as those guys have thier hands on engines every day that have more hours than I will put on all my boats in a lifetime.

[eseyoung]

As verified with a stethoscope my knocking (at idle) was at the injectors, which is metal on metal, lubricated by fuel. when the injectors of a CRD close they do so with considerable force, they have to, rail pressure is in excess of 15000#. The fuel is used as the lube for this contact.

I am interested in this and would love to hear what everyone else thinks on this i am not an expert, on much of anything really (but i am pretty good at drinking beer). but i know what i hear when an engine is running, more accurately, I notice when something changes. WHat do the guys at BoatDiesel say? Honestly, mechanical diesels are new to me. perhaps because of the lower FP they aren't as sensitive to variations? this is the only time that i have ever read (and i have read much on the topic) some actually prefer 'dirt' free diesel. Why is that?

for the boat i may or may not run something, i will try it and see if it makes a difference. for my CRD truck i think i'll stick to my 2stroke oil...250,000ish miles and 9000ish hours on original pump and injectors. I am going to keep doing what i am doing.

[RobS]

Everything I recall reading on BD was clean fuel, top notch filtration, no additives.

[denchen]

Like eseyoung I add two stroke oil to my car, a Mercedes and my 25ft Albin with a 1970s engine,as I am sure they both run quieter and give a smoother output.