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Old 02-13-2019, 07:02 AM   #1
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When is it time to replace exhaust hose?

The boat is a pilot house trawler style with cummins 6bt 220hp with 2000 hours.

This is a wet exhaust and the hose is about 20’. There are no visible leaks and I have not noticed any soft spots in the hose but it is almost 20 years old and I would hate to have a blowout underway. However I would like to avoid this job if possible. It appears the boat was built around this hose.

I would like to tap into the collective wisdom on this site to determine if replacing the exhaust hose is based on time, hours, or symptoms. Let me hear from you folks.

Thanking you in advance.

“Steelydon”
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Old 02-13-2019, 07:53 AM   #2
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I don't think time has much to do with it. Service conditions like temperatures do.

Since you have quite a length of hose to replace and it will probably be a chore, it might be worthwhile to collect some data about its service first. Let's assume it goes straight from the mixer to the transom. If there is a water lift muffler first, then the following is irrelevant- the temps will be low and constant in that case.

Get an IR gun and with the engine warmed up and in gear at the dock tied up at about 1,200 rpm to put some load on it, shoot the temps on the top of the hose every foot or so particularly the first 3-4 feet after the injection elbow.

Any temps that approach or exceed the 250 deg F rating of the hose should be cause to replace the hose.

Then you might want to look into why the temps are so high. Maybe blocked water holes in the injection elbow, or maybe just the geometrydoes it.

You can buy a higher temp blue silcone hose good for 350 deg, but it will cost a fortune- about $100/ft, normal black hose is about half of that.

David
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Old 02-13-2019, 10:57 AM   #3
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David has a good idea on testing. However, most of the black exhaust hose has a rating of 200 degrees F continuous and 250 degrees F intermittent. Exposure to high temps over a period of time can cause interior delamination of the hose (not visible from the outside) which, in the worst case scenario result in a sudden failure with exhaust gases and hot seawater leaking into the boat. Normal temps on the exhaust hose should be 100 - 120 degrees F. (certainly well below the rated 200 degrees). Here in Canada (where our prices are generally higher than US) the black hose sells for $35 - $50 dollars a foot for 5 inch hose (cheaper for smaller).
While you are examining your exhaust system (and after you are sure the hose is good) install a Borel exhaust hose alarm. This is inexpensive ($75) and will give an alarm warning of a problem (overheat) before any real damage is done! Saved me big time!
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Old 02-13-2019, 11:52 AM   #4
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I found out it was time when the aft cabin filled with water. Like an idiot I kept running the engine so the bilge pumps would get electricity. When I found out what it was I shut the engine down and the pumps including my wife manning (womanning?) the Edison portable caught up. The 4" X 24' hose had snapped in an unsupported area in a locker. This was in 1997 so the Taiwanese hose was 20 years old.



I replaced it with two 12' sections and a fiberglass connector. The hose was purchased from a local business that makes them (Trenton Hose). They are incredibly expensive to purchase from any of the normal marine suppliers and shipping is a biotch.



I picked the hose up and installed myself. Looks hard but it really isn't. Character builder was pulling the hose off the transom outlet while in the water. For about 20 seconds I had 1/4" freeboard.


Trenton makes - the world takes.
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Old 02-13-2019, 12:40 PM   #5
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Tom and David I have a gauge located just past the cooling water entry on the elbow that provides constant measurement during operation and an alarm that sounds at 210 degrees. I am just concerned about the effects of time on the hose and does the hose just wear out. Due to location I am in no hurry to replace unless age is a factor. I don't want to end up like Al. I will take the IR gun downstream from the elbow and see what I'm reading.


Thanks,
Don
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Old 02-13-2019, 01:09 PM   #6
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Don,
For answers to your questions regarding "life expectancy" of the hose, may I suggest contacting various hose manufacturers, and/or a surveyor, and/or a respected mechanic? Maybe go onto sbmar.com forum and ask Tony Athens, a very respected diesel expert.
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Old 02-13-2019, 01:19 PM   #7
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Quote:
Originally Posted by steelydon View Post
Tom and David I have a gauge located just past the cooling water entry on the elbow that provides constant measurement during operation and an alarm that sounds at 210 degrees. I am just concerned about the effects of time on the hose and does the hose just wear out. Due to location I am in no hurry to replace unless age is a factor. I don't want to end up like Al. I will take the IR gun downstream from the elbow and see what I'm reading.

Thanks,
Don

Immediately after the water injection point the water and exhaust gas swirl and mix. I have found that immediately after the injection point, the hose is maybe 160 degrees but a foot or two downstream it will jump to 200 and then finally four feet downstream it is fairly constant at maybe 150, implying that the gas and water have fully mixed.


So your gauge temp is only one point and it doesn't tell the whole story about hose temps.


David
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Old 02-13-2019, 01:30 PM   #8
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Yes, it only measures at one point, but it will tell you if you lost the cooling water before the hose burns through.
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Old 02-13-2019, 01:39 PM   #9
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Duh, calling the manufacturer makes a lot of sense. This is why I asked you guys. I will post the reply.


Thanks,


Don
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Old 02-13-2019, 04:25 PM   #10
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I spoke with Shields Hose which is a part of Seastar. Their exhaust hoses are sold with a limited lifetime warranty and do no require replacement unless damage is caused by owner. Overheating, physical damage,etc. So it appears that the hose is not a maintenance item but one that needs an regular examination.

Thank you for you help and comments.

Don
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Old 02-13-2019, 06:04 PM   #11
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Leakage and festering are 2 indicators. Usually they fail slowly with indications like drips and salt residue. Sudden failure is possible I suppose but less likely.
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Old 02-13-2019, 07:54 PM   #12
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IMO, it all depends upon the operating conditions, abuse due to over heating the hose and chafing. Engine hours on the hose are a suggestion or a caution. Investigating the hose with a IR thermometer sensing gun will tell you far more than reading the charts for engine hours. ie, I suspect, the engine hours on the hose will be less if traveling WOT as opposed to traveling at 6 or 8 knots. The same holds true for the exhaust elbow. Dont abuse anything..... it will come bite you in the ass if you do.
Install the Borel temp system, cheap insurance for your engine AND it gives us another meter to read on the long runs too.
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Old 02-14-2019, 09:24 AM   #13
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Age date?
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Old 02-14-2019, 11:17 AM   #14
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Some hose is fine at 40yrs, some is degraded in 10.

Go hand over hand the whole thing. Feel and look for soft spots, cracks, kinks, rusted wire (if wire wound), blistered areas, etc. If it looks good and feels good, I'd have no problem leaving it be.
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Old 02-14-2019, 04:20 PM   #15
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Firehoser is right on, before you call, be sure you get date mfr from the hose wall. Since hours are likely unknown, I'd replace at mfr's or experts suggested interval. Hose that lays around a warehouse ages as well, so be sure you don't buy "old" hose. Check mfr's date. Although I love NOS in many instances, this is not one of them...
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