Need to understand cooling system

dwleo

Cadet
Joined
Jul 10, 2012
Messages
18
OK.
I have a volvo-penta inline 6 cylinder with a screwed up exhaust manifold (leaky water jacket). A proper manifold will cost twice (at least) what the boat is worth. We got the boat as a 2 year 'work boat' to haul materials to a cabin we were going to start to build this year. The cabin is 10k from the marina. After it was done we were going to upgrade to a newer, nicer boat.

Now, how important is the cooling jacket around the exhaust? I realize it is there to cool the exhaust before it exits the engine but could one bypass the manifold and still keep the rest of the circulation? I am looking to find a way to keep the boat for the foreseeable future and maybe limit the speed.
What is the worst-case-scenario in this setup? Thanks.​
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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51,399
Re: Need to understand cooling system

the water jacket on the exhaust keeps the temperature below the point where fires and explosions start. you do NOT want to bypass the exhaust manifold. the worse-case scenario is your boat catches on fire, explodes, and kills people. the best-case scenario is your boat catches on fire and doesnt explode. in either case, your looking at a fire.

you have a few choices - sell the boat with proper disclosure, or get a new manifold.
 

Don S

Honorary Moderator Emeritus
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Aug 31, 2004
Messages
62,321
Re: Need to understand cooling system

Now, how important is the cooling jacket around the exhaust? I realize it is there to cool the exhaust before it exits the engine but could one bypass the manifold and still keep the rest of the circulation?

You MUST have that cooling water on the manifold. Without it, the manifold at speed will glow red/orange from the heat produced by the exhaust, and that is just to hot to be inside a closed engine compartment in a boat. Wouldn't be long until you had a fire or explosion, or both.
 

dwleo

Cadet
Joined
Jul 10, 2012
Messages
18
Re: Need to understand cooling system

That's what I was afraid of.
Thanks.
BTW - $3500 - $4000 for the manifold.
 

Don S

Honorary Moderator Emeritus
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Aug 31, 2004
Messages
62,321
Re: Need to understand cooling system

Everything else on those old 6 cylinder engines are just as expensive. Keep that in mind.
 

Maclin

Admiral
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May 27, 2007
Messages
6,761
Re: Need to understand cooling system

If you did bypass the manifold somehow to get the spent cooling water back out to the drive, several not good things would happen.

The large rubber hose that connects the riser to the exhaust tubing needs water in the exhaust spray to keep cool enough to not melt. If it melts then hot exhaust goes right into the engine house. The (uncooled) exhaust manifold itself would get way too hot also for being inside that tight of an engine house, I do not want to think of how bad that could get.
 

Maclin

Admiral
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May 27, 2007
Messages
6,761
Re: Need to understand cooling system

I started my post before I saw Scott's and Don S replies, then the wifey came by for the morning chat....!!! Sometimes I type slow, but not THAT slow...:D
 

diesel1960

Petty Officer 1st Class
Joined
Jul 3, 2012
Messages
205
Re: Need to understand cooling system

I do have spare one of this,where are you located ?
 

dwleo

Cadet
Joined
Jul 10, 2012
Messages
18
Re: Need to understand cooling system

I do have spare one of this,where are you located ?
Will give you good price,but part is very heavy to ship.

72 lbs to be precise. I have decided, with the help of people on this forum and others, to rid myslf of this boat and get another, better one. Advance by learning and learn when to quit.
But the whole issue has made me uncomfortable with I/O and will probably look at outboards.
Thanks to all who put up with me on this project.
 
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