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post #1 of 5 Old 09-28-2013 Thread Starter
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Purpose of water cooled exhaust manifold?

Thread diving I ran across a thread "We're getting hosed" that compared price differences between boat parts and "other" parts and one post caught my eye. The question revolves around the $500 price tag of a Universal Diesel exhaust manifold compared to the $80 for a Kubota tractor casting. I'm on my second 5411 in my '81 Newport: The first suffered a warped and cracked head from overheating, and the replacement engine, though rebuilt and working fine otherwise, has the original cast exhaust manifold which is rotting from the inside out and late this season has refused to pass water any longer.

I took it to my local diesel guy and he looked at it and said I could tank it but likely as not the rot was so extensive that nothing would remain. If anything, the exhaust flange is in even worse condition. I'd like to replace the whole kit and caboodle and have been eyeing the kubota part, or stroking my chin at the idea of having a header made up by a local exhaust specialist, but I'm scratching my head as to the need for the water jacket.....

Since the tractor, with it's enclosure and similar conditions doesn't use a water-cooled manifold, what purpose does it serve on my auxiliary? I guess I can see it providing another source of heat for a non-existent hot water system, but it seems to be just another source of failure, both for itself and ultimately the entire engine, since a clogged passage prevents ALL the cooling water from circulating which ultimately leads to engine failure.

What am I missing?
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post #2 of 5 Old 09-28-2013
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Re: Purpose of water cooled exhaust manifold?

Rubber exhaust hose and plastic Vetus water muffler..... could be her answer. Add, that most marinized engines are well enclosed and have no other way to vent/ radiate heat like an exposed tractor engine.
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post #3 of 5 Old 09-29-2013
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Re: Purpose of water cooled exhaust manifold?

Without water your manifold and exaust will run red hot under full load. This will probably melt and set something afire.

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post #4 of 5 Old 09-29-2013
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Re: Purpose of water cooled exhaust manifold?

Quote:
Since the tractor, with it's enclosure and similar conditions doesn't use a water-cooled manifold, what purpose does it serve on my auxiliary? I guess I can see it providing another source of heat for a non-existent hot water system, but it seems to be just another source of failure, both for itself and ultimately the entire engine, since a clogged passage prevents ALL the cooling water from circulating which ultimately leads to engine failure.

What am I missing?
[/QUOTE]

As mentioned, big time heat build up with little air circulation. I had a 3-71 Detroit diesel and IIRC, the output side of the heat exchanger went through the exhaust manifold and then overboard through a hose on deck, which was also used for wash down. Just had to make sure it didn't accidently discharge into the bilge. The exhaust was a "dry stack" and radiated a lot of heat even though we always ran with the engine room hatch open.

Even being water cooled, the manifold got pretty hot after running at speed.

I think the water cooled exhaust manifold is vital, probably why the engine manufacturers spend the extra money on them.

Paul T
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post #5 of 5 Old 09-29-2013
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Re: Purpose of water cooled exhaust manifold?

Read this; Custom Exhaust Riser/Mixing Elbow | s/v Smitty (here's the raw URL, because SailNet keeps auto linking: http://svsmitty.wordpress.com/2013/0...rmixing-elbow/)

Genius, freakin' genius!


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USCG Licensed OUPV Captain, ASA 101/103/104/105/106/118 Certified Instructor - Also certified in Recreational Marine Electrical Systems
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