Cat 3208TA's exhaust elbow

[Sax]

I am replacing my complete exhaust system on my 1995 GB42 with Cat 3208TA's that have 4200 hours. I pulled the exhaust elbow on the first engine and found a considerable amount of oily, carbon build up inside the turbo housing and in the exhaust elbow. Is this normal for this engine or do I have something else I need to investigate.

 

[tiltrider1]

What rpm do you cruise at?

 

[Sax]

Normally cruise between 8.5 knots at 1300 RPM to 9.5 at 1500 RPM. Above 1600 RPM the boat starts to climb its wake and fuel efficiency really suffers. I do try to operate for a short period of time each day at higher RPM when I am in an area that I don’t have to worry about my wake.

 

[Pete Meisinger]

Not normal, investigate further.

pete

 

[Sax]

Hi Pete,

Thanks. Could you please expound on “not normal” and where you would suggest I start to “investigate further.”

 

[twistedtree]

I could be normal build up of soot, but worth checking a few things.


I'm not familiar with the 3208TA, but it looks like all the 3208 variants have a max RPM of 2800. Does your engine reach 2800 rpm or more at full throttle? If not, what RPM does it reach? If the engines don't reach full RPM at full throttle then they are over-propped and will likely soot faster than they should.


Do you know if the exhaust elbows and turbo outlet have been cleaned before, and if so, when? Just trying to get an idea whether this is a couple of hundred hours of build up, of 4000 hrs of buildup.

 

[Alaskan Sea-Duction]

CAT recommends you run 3208 T/A at 80% of WOT. In the winter, I do this 2 or 3 times. During cruising season I run at this at least 4 or more times.

 

[tiltrider1]

Minimum RPM for a cat 3208 is 1500. What you are seeing is exactly what I would expect of an engine that spends most of its life at 1300 RPMs.

Send the turbos out for service. In the future finish each run with 10 minutes at 2000 RPMs.

 

[twistedtree]

Minimum RPM for a cat 3208 is 1500. What you are seeing is exactly what I would expect of an engine that spends most of its life at 1300 RPMs.

Send the turbos out for service. In the future finish each run with 10 minutes at 2000 RPMs.

Really? I found a data sheet listed all the different power ratings and all said 2800 rpms. I actually found that surprising because engines I'm familiar with all have incrementally higher max RPM for each incremental HP rating. But other than looking at that datasheet and reading about various 3208s, I know nothing about them.


Would it be useful to know the HP rating for these GB engines?

 

[C lectric]

I am not a Cat expert or a 3208 owner but this has come up on B.D. many times.

I will guess that the TA means the engines are the 370 HP versions. Means those engines were installed to drive the boat at planing speeds of about 14-15 knots at about 2400 to 2500 rpms. THere were a lot of the G.B. 42 of that era so equipped.

You running at 1,300 rpm likely means the engines are not getting hot enough to cleanly burn the fuel or burn off the deposits building up on the piston rings and other areas.

Likely part of the problem is the intake system is likely not taking in quite enough air for a cleaner burn. THe turbos are likely not helping either.

Do you have a boost guage and what do they say at your 1,300 rpm?

Take a good look at the turbo blade to housing clearance on the hot exhaust side, NOT the air intake side. New it would have been about 7 or maybe 8 thousands of an inch . If it is much over that then the turbos are getting on. However they can operate adequately with more clearance than that. Just that the engines will smoke more than they used to.

As for suggestions about how to avoid a lot of the buildup [and smoking??] would be to take an inch or two of pitch out of the propellors so the engines must rev higher to maintain the same boat speed. THat will put more air through the engines meaning a better burn. You should not use much if any more fuel as long as the boat speed is the same.

Continue to run the engines at the revs needed to maintain your current boat speed. Maybe 1,400 to 1,500.

The engines will make the same HP as at the 1,300 revs and same boat speed but with more air going through the engine. EACH injection event will be smaller with more air as part of the event.

But it will take a repitch to do that.

You will also lose some top speed but it sounds like that is not of much importance to you.

In the meantime, I agree with the suggestion of run the engines up for about 10-15 minutes before going in for docking. Maybe about 2,000 revs.

That will heat the engines more and the increased exhaust will blow more of the accumulated soot out of the system.

And yes it would help zero in the suggestions if you told which model and HP of engine you have.

 

[Pat T]

FWIW, I have the 3208's rated for 435HP. Guessing with a 95 you might have the more common 375HP version but not sure it matters here. First thing I would do is look at the other engine and see what it looks like.
I replaced one of my elbows last year and it looked much cleaner than yours with no oily build up. Yes, some carbon build up but minimal. At that time I had about 500 + hours on rebuilt engines. The exhaust elbows may have been cleaned at the rebuild - don't know as I did not own the boat then. Further, I am able to hit 2800 rpm's and I do probably 80% of my cruising at 1400 rpm's. I also make it a point of trying to run up to at least 2000 rpm for at least 20 minutes every 4 hours but I do bump it up to 2400 every now and then too.
Good luck. Let us know what you find out.

 

[Sax]

I do have the 375 HP TAs. I have owned the boat for the past 1800 hours. During that time, I haven’t pulled the exhaust elbows. Don’t have any records on what the previous owners did. A lot of my hours were done on the Great loop, Downeast loop and up and down the ICW. Cruising on those trips involved a lot of hours on canals and inland rivers and that was typically done at slower speeds. I do blow out the engines at high RPM when I can.

I am replacing both wet exhaust systems while the boat is in the water. I don’t want to disassemble both engines at the same time in case I need to move the boat in an emergency. I will pull the port elbow after I complete the exhaust rebuild on the starboard side.

Thanks for your reply.

 

[Sax]

I have the 375 HP TAs. I don’t have EGT or boost gauges but will probably add them while I am doing this project. I currently come up a little short of 2800 RPM at full throttle. Concur with recommendations on taking some pitch out of the props. Probably won’t get around to re-pitching the props until I have some other reason to pull them.

 

[C lectric]

If you do go for boost and EGT guages consider the Turbocator By Isspro.
It is a 3" guage with both functions.
It is offered by Seaboard Marine in Oxnard but of course by others.

I'll leave you to look it up.

I have had the EGT on my V555M Cummins engine, single, not turbo, since I owned the boat and I will swear it saved me from destroying my engine.

 

[twistedtree]

I have the 375 HP TAs. I don’t have EGT or boost gauges but will probably add them while I am doing this project. I currently come up a little short of 2800 RPM at full throttle. Concur with recommendations on taking some pitch out of the props. Probably won’t get around to re-pitching the props until I have some other reason to pull them.

Then I would ask on BoatDiesel. I’m not convinced there is anything wrong at all, and that it’s anything more than years of soot buildup.

 

[luna]

Perhaps it's a water intrusion problem, which to fix would possibly require an exhaust routing redesign using as much height as the engine room allows.

Try this link. https://www.sbmar.com/articles/what-a-marine-diesel-turbo-should-look-like-when-inspected/

 

[Sax]

I am happy with the way the turbo and exhaust elbow cleaned up. As the old time watermen here in Poquoson, VA like to say..."it is good enough for who it is for." Since I have free rotation, no end play on the shaft, and no obvious oil leaking, it is going back together as is. Thanks everyone for your comments and suggestions.

 

[Deano]

My 3208s would run at1300 rpm’s and be very thrifty. Somewhere around 1400 the turbos would kick in and it was not so thrifty. I just would run the rpms up to where the black clouds started and run them that way until they disappeared. Every couple hours and no problems.

 

[JYoung]

Stupid question:

Why don’t you call someone who is a Cat dealer, or Cat authorized repair, or a real diesel mechanic with credentials and credibility who has experience with CATS? I have a 3208A on my GB 36C and they have all been extraordinary and not only sharing opinions.

 

[mpstan]

Twin 3208T 320hp in our OA42 sedan, also curious to know if the OP can make WOT 2800 RPM. We also run at 1300-1400. WOT for us, fully loaded with water and fuel, is 2400. We’ve been advised to clean the bottom, and repeat sea trial but our prop guy is thinking we need 24x22 props, compared to the 26x24 that we presently have. So replacing, not repitching….

 

[Sax]

Some answers to previous posts.

I did consult with a long time Cat mechanic who is now in business for himself. His response was that the accumulation of carbon behind the turbo in the exhaust elbow was not a cause for concern, particularly if the engines had habitually been cruised at lower RPMs. After getting his thoughts, I posted this question on this and other boat forums to get some additional opinions.

When I purchased my boat nine years ago, the engines made 2650 and 2825 during the sea trial on clean running gear, with a lightly loaded boat, on a sub freezing temp day. This reading was on the boat’s installed tachometers. For some reason, the mechanic from the local Cat dealer that I hired for the engine portion of the sea trail missed recording the max power tach numbers using his direct reading tachometer. I was not very impressed with what I got out of his engine survey.

When running the boat at max power over the years, I normally see between 2600 to 2700 RPM. (I made a chart correlating my direct, hand held tach readings with the boat’s installed tach gauges). Max RPM varies depending on weight on board, air temps, sea state, and fuel filter, air filter, and running gear cleanliness.

Both engines consume about a quart of oil every 15 hours. I am sure that contributes to the carbon build up in the turbos. Four years ago, I blew a head gasket on startup. That gave me a chance, during the repair, to see inside four of my cylinder walls. They are somewhat glazed. I can thank the previous four owners of the boat for also contributing to that condition. At this point, changing the way I cruise the boat, probably will not make a huge difference in engine life.

I also know that cruising at low RPM can result in too low oil temperatures, which can contribute to reduced engine life. A few years ago Cat addressed this problem with new engine regulators (Cat’s term for thermostats). The regulators begin to open at 192 degrees and are completely open at 207. I have installed these hotter running thermostats in both engines. My engine oil temps measured at the oil pans with a hand held infrared gun are over 190 degrees.

Concerning my props, I do not know the specific dimensions. Neither one is stamped. If I ever ding them, I may then explore sizing and pitch options.

The engines are obviously bigger than they need to be for this boat. When Grand Banks built it, fuel was cheap, time was precious and people thought having a fast trawler that could make 18 knots was what they needed. Although my boat will still make 18 knots, that is not the way I can afford or choose to cruise.

Thanks to all for sharing your opinions…that is what I was looking for.