6CTA discoloration on turbo, pipe, and cooler. Cause?

[John Easley]

Browsing through YachtWorld, looking for a potential new home, and ran across a boat with Cummins 6CTA 450 hp engines. Love the engines. First time I have seen this brown discoloration on the turbo, tube coming from the turbo, and the aftercooler. The photos provided in the ad don’t show the port side of the port engine, only the starboard engine. The engines have 740 hours on them. Any of you diesel mechanics run into this before? What are the likely causes? Is this something that would make you run away from that boat?

There are two photos attached. On the right side of the first photo, you can barely see the starboard engine’s turbo. It’s obvious that it is brown. So is the tube leading under the air filter to the cooler. The second photo is a close up of the aftercooler showing discoloration.

Thanks for any thoughts.

John

1 user thanked author for this post.

Bill kosky

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[John Easley]

Thanks, Rob. That’s a fine-looking boat you have.

[Rob Schepis]

Thanks. Great pic, that is one good looking very capable classic aft cabin cruiser!
Same wave slicing entry as my hull.
A couple of shots of my Chris were uploaded here:

https://www.sbmar.com/community/topic/welcome-to-the-seaboard-community/

[John Easley]

Nice sport fisher you have there. Ours was a 1986 42′ Catalina aft cabin.

[Rob Schepis]

Sounds like a plan. What Chris did you have? I’m running a ’74 36 Commander Tournament SF w/ 6BTA 330’s..

[John Easley]

Thanks, Rob. Yes, we’re more in the comfort cruising category. Our most recent boat is a 42’ Chris Craft that was repowered with 330 hp 6BTAs. Loved those (except the impeller/raw water pump location). Our typical approach to travel is to run it up to about 2300 rpm for about five minutes after we hit open water and then back down to about 8.6 knots or 10 mph for the rest of the day. Smooth, comfortable, wonderful fuel economy. We’ll be taking the same approach with the next boat. At the moment, we’re pretty settled on the 53’ Carver Voyager Pilothouse with 6CBTs. Should meet all our needs.

[Rob Schepis]

John, your initial post stated, ” looking for a potential new home”. So, are you interested in cruising comfort and not the fast cruise? She’d make a great maneuverable trawler with some “get-up” at times for fighting a ripping current, etc..

[John Easley]

Great information! Thanks for the clarification, Tony and Phillip. If we are looking at a boat with such discoloration, we will ask more specific questions about the use and maintenance before making a decision about walking away or not.

[Tony Athens]

John,

All of the responses above are “right-on”, but the one that hit it on the nail head is Rob’s………..IMO, this is way too much boat for 450 Diamonds if you want to try and run on plane…. Even if propped to make 2700 RPM ( 100 over the MINIMUM RATED RPM) , if you are running on plane, at lets say 18 kts or so, these engines will need to run at at 17-20 GPH per engine probably making 20+Lbs of boost.. Sure, engines will do this, but do not expect them to do it for 1000’s of hours…..

This is a nice boat and the engines are world class with very low engine hours. The “dark brown” just indicates that the past operator liked to go fast and the compressed air leaving the turbo was in the 300++ F range causing the white paint to burn. ..So, you could call that “normal”.

As Phillip said, this should not be a deal breaker.. It really just comes down to your needs for a vessel like this and what you are willing to do to make sure that if you do want to travel well above hulls speeds, that you do what needs to be done to make all as right as it can be….

Tony

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[Philip]

Pushing vs propping

John –

A point of clarification. When people usually reference “Pushing” they think “doesn’t matter what the pitch of my props are if I don’t “push” the engines hard aka keep the RPMs low then all is good – totally false way of thinking. And engine that is overpropped and doesn’t make max+ rpm is overloaded at all RPM’s.

This is real important to understand for any boat.

1. The engine doesn’t care what the pitch of the prop is and for the record most brokers and owners don’t really know even if they tell you. And most boats come from the factory overpropped anyways. The engine only cares how easy it is to turn. Yes that’s related to pitch and that’s how most owners think of it but the engine only feels the load as it tries to turn.

2. If you are propped correctly i.e. You can make max+ rpm easily the engine will not be overloaded at ANY rpm and there is no way to “push” the engine hard.

Read this a few more times….

Propping a Cummins Mechanical Diesel Engine

[John Easley]

Okay, so some is normal. But the photos in that YachtWorld ad depict what appears to be more than normal and seem to indicate the engine has been worked harder than necessary. Could be over-propping (the broker didn’t list the pitch of the props on that particular boat or any details about the servicing record) or pushing the engines too hard or lack of proper maintenance. Interesting. We regularly pushed my 36,000 lb boat on plane with 6BTA 330 hp engines and never saw any discoloration but we stayed on top of maintenance, too. Thanks for the speedy responses. Good food for thought.

[Rob Schepis]

Some “tanning” of the turbo and air pipe is normal. Cooked dark brown all the way into the aftercooler is not.
BUT…Overpropped or not, that is what you are going to see trying to run a 50,000 lb vessel “on-plane”. Way too much boat for that for these engines to live a long life…

[Philip]

Two Causes….

John,

It’s normal to see some light tanning of the turbo, tube, and even the first part of the aftercooler but from the limited views of the pictures you posted that is WAY more than normal tanning.

There are two causes of this:
1. Overpropped – Spend some time reading on this site on how properly pitch props for max RPM especially with the 450hp version of this engine. Do you know the max RPM these motors make?

2. Lack of PROPER aftercooler servicing – Again spend some time reading about marine age and proper off engine aftercooler servicing. Does the seller have any maintenance history on that?

Not necessarily a deal breaker but not enough info yet to say anything more. Get the answer to these questions and some complete pictures of the engines in high resolution (so we can clearly zoom in for details) from ALL angles especially the turbo and complete exhaust setups.

Phil

Propping a Cummins Mechanical Diesel Engine

Cummins Marine Aftercooler Maintenance

Aftercooler Discoloration from High Loads or Turbo Boost

Everything you Need to Know About Marine Exhaust Systems

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