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Old 19-09-2017, 06:17   #1
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Discoloration on engine exterior. Causes?

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 cooler. 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?

Thanks for any thoughts.

John

On the right side of this 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.


This close up of the cooler shows discoloration.
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Old 19-09-2017, 06:56   #2
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Re: Discoloration on engine exterior. Causes?

It seems normal (and our tech agrees) for the 6CTA turbo and the inlet pipe to discolor like that. Simply a matter of high temps versus paint.

Our aftercoolers have not exhibited that same symptom, though.

The specified aftercooler maintenance regime is flushing (the raw water side) every 300 hours or one year, whichever comes first.

More complete periodic service would be to remove the units and "flush" both raw water and air sides. Can't find the spec on that service just now, but we've done that every 300-400 hours or so IIRC.

Might be the discoloration on the cooler in the pic suggests higher temps there than normal.... which might in turn suggest lack of periodic service.

That's just speculation, though!! Would be better to get more informed info from a real Cummins tech.

-Chris
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Old 19-09-2017, 08:57   #3
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Re: Discoloration on engine exterior. Causes?

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Originally Posted by ranger42c View Post
It seems normal (and our tech agrees) for the 6CTA turbo and the inlet pipe to discolor like that. Simply a matter of high temps versus paint.

Our aftercoolers have not exhibited that same symptom, though.

The specified aftercooler maintenance regime is flushing (the raw water side) every 300 hours or one year, whichever comes first.

More complete periodic service would be to remove the units and "flush" both raw water and air sides. Can't find the spec on that service just now, but we've done that every 300-400 hours or so IIRC.

Might be the discoloration on the cooler in the pic suggests higher temps there than normal.... which might in turn suggest lack of periodic service.

That's just speculation, though!! Would be better to get more informed info from a real Cummins tech.

-Chris
Thanks, Chris. I'll post the same photos over on sbmar.com and see what they have to say.
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Old 19-09-2017, 12:27   #4
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Re: Discoloration on engine exterior. Causes?

It's not unusual for air temps coming out of the compressor side of the turbo to be as high as 350 degrees F, and it's this temp that is causing the turbo housing and air pipe paint to discolor. You can see that the aftercooler is doing its job cooling the air down, as the discoloration fades away.

Plenty of other engine brands do the same thing.

DougR
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Old 22-09-2017, 06:05   #5
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Re: Discoloration on engine exterior. Causes?

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Originally Posted by DougR View Post
It's not unusual for air temps coming out of the compressor side of the turbo to be as high as 350 degrees F, and it's this temp that is causing the turbo housing and air pipe paint to discolor. You can see that the aftercooler is doing its job cooling the air down, as the discoloration fades away.

Plenty of other engine brands do the same thing.

DougR
Thanks, Doug. I contacted Seaboard Marine, who are big into Cummins engines and repowering. They advised the same thing. Such discoloration is not, in itself, a reason to back away from a boat but it certainly is cause for asking a few more questions. Tony, at Seaboard, said it was most likely indicative of the current owner running the boat at near wide open throttle for extended periods of time. Makes sense. We typically run ours at about 70% throttle for five or ten minutes and then back down to hull speeds for the rest of the journey and we've never seen any discoloration.

My guess is we hadn't seen such discoloration in ad photos before because a lot of people spray paint the engine, often sloppily, before putting the boat up for sale. At least this seller was honest and didn't try to hide the discoloration.

Good learning exercise. Thanks for all of the input.
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Old 22-09-2017, 08:21   #6
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Re: Discoloration on engine exterior. Causes?

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Tony, at Seaboard, said it was most likely indicative of the current owner running the boat at near wide open throttle for extended periods of time.

Interesting. We often putter around at slightly under hull speed, but even when we travel on plane for extended periods we usually run at only 2200 RPMs, very occasionally at 2400... with our rated (and achievable) WOT being 2600.

-Chris
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Old 22-09-2017, 09:19   #7
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Re: Discoloration on engine exterior. Causes?

It may be the paint. I have seen 2x polyurethane turn that color on air cooled cylinder heads, they get to 350+. Regular engine enamel does not do that.
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Old 22-09-2017, 09:51   #8
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Re: Discoloration on engine exterior. Causes?

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It may be the paint. I have seen 2x polyurethane turn that color on air cooled cylinder heads, they get to 350+. Regular engine enamel does not do that.
Interesting. Wrong type of paint used. Hmm...
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Old 22-09-2017, 11:01   #9
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Re: Discoloration on engine exterior. Causes?

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Interesting. Wrong type of paint used. Hmm...

Some times it's too much of a good paint that turns colors. I'm not sure you could say Imron is the "wrong paint" but it will turn color if there is too much of it.
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Old 22-09-2017, 11:04   #10
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Re: Discoloration on engine exterior. Causes?

I've seen more engines like that than not. Almost all commercial engines look like that
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Old 23-09-2017, 10:20   #11
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Re: Discoloration on engine exterior. Causes?

Quote:
Originally Posted by Guy View Post
It may be the paint. I have seen 2x polyurethane turn that color on air cooled cylinder heads, they get to 350+. Regular engine enamel does not do that.
Quote:
Originally Posted by JohnEasley View Post
Interesting. Wrong type of paint used. Hmm...

Color rendition on the computer probably isn't perfect... but it looks like Cummins paint to me. The (Cummins) paint on our aftercoolers hasn't turned like that.

-Chris
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Old 23-09-2017, 10:36   #12
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Re: Discoloration on engine exterior. Causes?

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Originally Posted by ranger42c View Post
Color rendition on the computer probably isn't perfect... but it looks like Cummins paint to me. The (Cummins) paint on our aftercoolers hasn't turned like that.



-Chris


But by your own admission you don't run hard.
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Old 23-09-2017, 10:37   #13
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Re: Discoloration on engine exterior. Causes?

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Originally Posted by ranger42c View Post
Color rendition on the computer probably isn't perfect... but it looks like Cummins paint to me. The (Cummins) paint on our aftercoolers hasn't turned like that.

-Chris
Nor on mine.
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Old 23-09-2017, 11:11   #14
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Re: Discoloration on engine exterior. Causes?

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But by your own admission you don't run hard.

Yep, true. OTOH, when we're on plane I'm running the engines as recommended by Cummins.

-Chris
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