Exhaust manifolds and risers, how are they plumbed inside?

[ricohman]

Sounds like a dumb question, but I'm an auto mechanic. I've owned my boat for the season and I still don't know exactly how the risers and manifolds are plumbed and how they cool the manifold.
I am curious as I was wondering how a 4.3 could injest water through the exhaust by running reverse rotation. My 2011 4.3TKS backfired through the carb and sputtered to a stop while fogging. Running on muffs.
Where do the water and the exhaust meet? Does the water get pumped to the top and then gravity takes care of the rest?

 

[haulnazz15]

Re: Exhaust manifolds and risers, how are they plumbed inside?

It's just a set of exhaust manifolds with a water jacket around it. The water and exhaust don't "meet" until they exit at the end of the riser tube which dumps into the y-pipe. Reversion occurs when the exhaust flow is low and the momentary inward pulse from an engine with lots of lope in the cam pulls in the water at that point. Also possible when exhaust shutters aren't present and water is forced up the exhaust tube from outside the boat and into the open exhaust ports.

 

[ricohman]

Re: Exhaust manifolds and risers, how are they plumbed inside?

It's just a set of exhaust manifolds with a water jacket around it. The water and exhaust don't "meet" until they exit at the end of the riser tube which dumps into the y-pipe. Reversion occurs when the exhaust flow is low and the momentary inward pulse from an engine with lots of lope in the cam pulls in the water at that point. Also possible when exhaust shutters aren't present and water is forced up the exhaust tube from outside the boat and into the open exhaust ports.

OK. Then the chances if my 4.3 injesting water from a backfire seem pretty slim. But I can see how water could be injested from a run-on situation in the water. But it may take more than a second or two.

 

[Don S]

Re: Exhaust manifolds and risers, how are they plumbed inside?

From a single backfire, yes, pretty slim. But you did right by restarting for a few seconds to be sure.

 

[ricohman]

Re: Exhaust manifolds and risers, how are they plumbed inside?

Having all that water above the ports would mean water in the cylinders if a crack ever appeared. How long do manifolds last? Is it something an i/o owner should inspect or replace at a specified interval?

 

[Bondo]

Re: Exhaust manifolds and risers, how are they plumbed inside?

Having all that water above the ports would mean water in the cylinders if a crack ever appeared. How long do manifolds last? Is it something an i/o owner should inspect or replace at a specified interval?

Ayuh,.... In freshwater, they'll last darn near forever, or until their frozen with water in 'em....

In Saltwater, I hear 3 to 5 years,... The gasket surfaces, 'tween the manifold, 'n riser rusts/ erodes away...

 

[Don S]

Re: Exhaust manifolds and risers, how are they plumbed inside?

In Saltwater, I hear 3 to 5 years,... The gasket surfaces, 'tween the manifold, 'n riser rusts/ erodes away...

:facepalm: Even in salt water they last at least 5 years in 99% of the cases (that other 1% is owner problems). But he also has the "Dry Joint" exhaust. You don't have the gasket surface problems of the old style manifolds.
The risers will clog up and the engine will overheat long before you would get water into the engine on that system.

Even trailer boats in salt water that flush engines after each use get 8 to 10 years if they flush them right.

 

[Bondo]

Re: Exhaust manifolds and risers, how are they plumbed inside?

:facepalm: Even in salt water they last at least 5 years in 99% of the cases (that other 1% is owner problems). But he also has the "Dry Joint" exhaust. You don't have the gasket surface problems of the old style manifolds.
The risers will clog up and the engine will overheat long before you would get water into the engine on that system.

Even trailer boats in salt water that flush engines after each use get 8 to 10 years if they flush them right.

So is 5 to 8 a Safe statement,..??

I'm just an internet mechanic, so I wanta get it Right ya know......:redface:

 

[Don S]

Re: Exhaust manifolds and risers, how are they plumbed inside?

5 Years would be a safe bet as to when to start removing the elbows and actually inspecting the gasket surfaces on the old style manifolds and elbows. Not just a blanket statement that they need to be replaced at X to Y years of age.
Too many newbies replace things that shouldn't be replaced just because someone on a forum says it should be replaced. To many posters just repeating and embelishing what they hear without knowing anything first hand.