Marine Exhaust Manifolds. How Do They Work?

Hey Everyone, Today I go over a boat exhaust manifold and show how they work and how the water cools them. I cover all the basic components of a Marine manifold.

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[clintperez]

Excellent job explaining this. Not knowing what a mechanic means when they say this ir that is bad, your explanation makes it crystal clear

[smhaceofspades]

Cool deal man I work night security at a marina so I see the stuff but no clue what it is and this definitely answered 101 questions.

[gcrauwels]

Just had a Volvo Penta GL 4.3 where an old impeller failure sent fragments into the thermostat, clogging the fitting to the manifold feed on one side. Absolutely roasted the two rubber hoses on the discharge. Even melted the alarm switch.
Always check for failed impeller blades.

[MikeSsuncoasttrains]

The tiny holes are for water to escape. The manifolds have a built in heat exchanger where water stays in the the jacket around the manifolds to help keep them cool. The water escapes slowly out those holes along with the engine hot water. On the older log style a hose goes to the front and back and has one tiny hole in the restriction plate. A separate hose goes on top of the riser from the water pump. On these the water goes in from ends to end and water pump water comes out thru the bottom thru the big holes out the riser.

[Bierdaddy]

1987 Bayliner 2450 Ciera with an omc GM 5.7 with a similar open cooling system. Thank you for giving me a new maintenance project, like I don’t have enough. 😆 You saved me $$$ by giving a diy amateur a bit of good know-how. Thank you. 🍻

[portagepete]

While idling out in the water tap your hand on the risers make sure one is not hotter or too hot, one time I had a boat where the water jackets inside the risers were so full of rust NO water was getting through. After checking the price for another one I just got a long drill bit and cleaned all the rust out.

[AndieBlack]

Perhaps it would be beneficial to point out just why marine exhausts are so different from car exhausts. One could think that car exhausts are essentially air-cooled & marine exhausts are water-cooled. Why is this? The marine engine bay is a fully enclosed space, the automotive spaces are open to airflow. The car uses air thru the radiator AND along the exhaust manifolds to extract heat, the marine engine only uses a body of water as the source to extract heat.

[mikedodd]

A wet joint exhaust is shown in this video. Older style. The fuel injected engines found in boats from at least 2000+ use a dry joint which don't have this design flaw where it can leak into the engine and seize the engine. You could still lose an engine with a dry joint exhaust but it not as common. Replace them every 5 years in salt water and you'll never have to worry.

[timjohnson]

Thanks for taking the time to make this video. Very informative.

[researchcapt]

Thanks. Now I have an idea of what I am up against with changing my Mercruiser manifolds.

[RoyBowen]

Been saving this video for a couple months so that I could reference it with an upcoming riser maintenance job on my 2006 Volvo Penta 4.3gl (I bought it used a few months ago). Unfortunately, I'm now being forced to do this job sooner than I expected because last weekend while in the Gulf, we were cruising FOT and I stood up to readjust my seat but forgot my safety strap was clipped to my shorts. Ignition cut out as expected but then I couldn't restart the engine no matter what I tried. Thought maybe it was the battery died suddenly or starter even. Had to get a tow boat. He tried jumping but the battery was fine. Starter just clicked with no engine turn over so he towed us back in. When I got home I took out the plugs and turned the starter and 2 cylinders shot water out like a cannon. Talked to some boat mechanic friends and they claim the water must have came up backwards through the exhaust system and fed down through whichever cylinder valves were open at that time. Anyone else experience this issue?? Is it common? I should mention that I have raw water cooling. Thankfully, after a few days of turning it over using the starter plus some fogging oil and ensuring there's no water in the engine oil, I was able to get it dry and get it running again. Obviously, I'm nervous about this happening again! I don't think I have any cracks or water in the manifolds but this weekend I'm going to take the risers off to check that and probably replace them since they are original and exposed to saltwater.

[brendanbockelman]

Thank you so much!!! I am learning too work on my boat. Couldn’t figure out my water in oil until you helped me!!! Thankyou so much

[thomaspaccione]

I just did this job on my boat today. My boat is raw water cooled, and only used in salt water. Mine rotted internally causing a pathway from the water jacket into the exhaust path. Water was then leaking into my exhaust ports. I find that I need to replace these every 6 years or so. Mercruiser now makes these with ceramic coating on the inside to keep them from rotting internally.

[rdprdputube]

I've been told the gasket with the 2 small holes are used on the most common open systems where sea water comes in thru the system and goes out the exhaust. If you have a closed system the gasket is different and the holes are open.

[GearHead]

Thank you! I had 2 mechanics tell me that I had a blown head gasket (water in oil) pulled my 3.0 all apart and found the head gasket wasn’t bad (tested with good compression on all 4). My riser/ manifold were the base of all my problems.

[crixusinhowolf]

very very nice video.no stupid music and everything is nicely filmed and explained. thank you dude

[wesleyadams]

Thanks for the explanation. I just replaced my '97 model 4.3 Mercruiser V-6 engine in my boat due to the thermostat not opening during winterization and not getting any antifreeze into the block. Lesson learned. I have the 1-piece manifold/risers. Fortunately they seem to be ok. I have taken the boat out a couple of times with no issues thus far.

[buzzedalldrink]

very interesting Seems to me if they made the exhaust manifold with a flange that fits up into the riser that would eliminate the possibility of ever having an internal leak. As you said water cannot flow up hill. Just my $.02, I am a car guy. I know nothing about boats. This is actually the first time I have ever seen one of these.

[truthseeker]

Nicely done. Very nicely done.

I was looking for 8.2L Mercruiser cooling system info and I came across this. I'm essentially looking for info in regard to how the entire cooling system functions; I do have a basic understanding of it but I want to know the intricacies of it. Knowledgeable and trustworthy marine mechanics can be difficult to find. I want to understand the system top to bottom/front to rear so that I don't have to wonder if someone knows what they're doing. This does help somewhat. At least now I know that the exhaust manifolds are water-jacketed using sea water, very similar to an engine block being water-jacketed and using engine coolant.

Thank you for doing this.

Subscribed!

[niklaso]

Thank you for this video. My boat started is blowing white smoke and running bad. Probably the risers.