What is the Functin of the Manifold?

[milkyway]

In one of my posts, someone posted that the " manifold could have died". My post was about the starboard manifold and elbow becoming hot while the port side is cold. What does the manifold do? Does it have any mechanical functions or does it merely diverts exhaust fumes from the engine to the exhaust pipe? Just curious what I should expect to see and look for when I take down the manifold and elbow for inspection.

 

[Boomyal]

Re: What is the Functin of the Manifold?

The exhaust manifold is just that, a means to remove combustion gases from the cylinders. The marine twist is that because there is no airflow over the exhaust manifold, as in a auto, the manifold is constructed to flow cooling water between the actual manifold and the outer housing. The flow of water is usually controlled by orifaces in the 'elbow' whose purpose is to eliminate the reversion of water from out side the boat back into the engine. If your elbows are rusted up, water will not flow thru them and they will get hot. <br /><br />Manifolds and elbows have a very finite life, especially when used in salt water.

 

[milkyway]

Re: What is the Functin of the Manifold?

Very helpful info. Thanks.

 

[milkyway]

Re: What is the Functin of the Manifold?

Okkk, I have removed the elbow and manifold. Noted rust formations in all passages.<br /><br />To test for obstruction - - - Ran water from the hose to holes on one side of the elbow and water came out of the other holes in the elbow without problem. Then I inserted the hose to the bottom of the manifold where the hose from the thermostat is connected and also which has the water release valve, water came out freely to all holes of the manifold. I put the manifold on one side and noted water flowing freely. Then turned it on the other side, free flow again. Ran water through the hose that is connected to the manifold, no obstruction. I inserted the water hose to that large round pipe that was connected to the end of the elbow and water flowed freely in the outdrive - no obstruction. So why are the starboard elbow and manifold so hot while the port side is dead cold when engine is running? Why do I get a lot of steam on the outdrive ( starboard side) and less and less water as the months went by? <br /><br />Can someone help here? I'm stuck. I hope I did not make a big mistake removing this thing which is so heavy.

 

[Don S]

Re: What is the Functin of the Manifold?

As I recall, you replace the port side manifold and riser, is that correct? If so, what is happening is the new manifold and riser have less restriction, rust, and corrosion. Therefore there is better flow, and the water chooses the path of least resistance and this causes the one side to get less flow. <br />To prove this, just put the new riser and manifold ot the other side and see if your problem changes sides. (it probably will if that is the cause of your problem) if the problem still exists on the starboard side, then you have a different problem. But at least you have eliminated one possiblility without buying more than a few gaskets.

 

[milkyway]

Re: What is the Functin of the Manifold?

NO, I have not replaced yet the starboard manifold and elbows. When this 1999 maxum boat was surveyed last May, the surveyor reported 30 degrees rise in the no. 3 cylinder of the exhaust manifold. Does this help? Water and exhaust gas flow together in the 4 or 5" exhaust pipe, right? Can't do now removing the port side. I am already overwhelmed by the weight of this thing.

 

[milkyway]

Re: What is the Functin of the Manifold?

In this large pipe that is connected from the elbow to the outdrive, is water supposed to flow out together with exhaust gas? It seems that they do. What could be the reason I have steam coming out with water?<br /><br />Can anyone give me some additional possible hints about why I have hot starboard elbow and manifold?<br /><br />IMO, there is sufficient flow of water in all passages of the elbow and manifold and no major restriction.

 

[milkyway]

Re: What is the Functin of the Manifold?

I read from other posts that water and exhaust flow "together" from after the elbow to the outdrive. My question has been answered. <br /><br />I have raw water cooling system, 1998 5.0L 220 HP mercruiser, alpha gen II.<br /><br />Can anyone give me some additional possible hints about why I have hot starboard elbow and manifold? I think I'll just put this back this weekend if I get no resolutions.

 

[butlp]

Re: What is the Functin of the Manifold?

Not sure if you are talking Mercruser or Volvo but I had a similar problem with my VP.<br /><br />Firstly, are you performing all of your tests using the muffs or boat in the water? You may not be getting sufficient water using the muffs and as stated above the water will take the path of least resistance.<br /><br />My sea water pump impeller started to disintegrate and small bits of rubber went through the cooling system and blocked off the feeds from the thermostat to the manifolds. My manual says to disconnect the feed to the thermostat from the sea water pump. Hold it vertically level with the thermostat housing and then start the engine for less than 30 seconds. You should see a column of water at least 4 inch's high coming out of the hose. If you don't then you have something wrong with the sea water pump or a blockage/leak in the hoses.<br />If the pump checks out OK then disconnect the feeds to the manifolds and repeat the process. if there are no blockages in the thermostat housing or hoses then you should see a similar column of water out of each manifold feed hose.<br />Again, do not run the motor for more than a few seconds with any of these hoses disconnected.<br />Finally in my case the manifold had overheated enough to burn the exhaust bellows and the flapper valves. Volvo use a rubber valve and Merc use a rubber coated metal valve which I believe is more durable. You may want to check them and make sure there are no flapper valves stuck in the exhaust system that could restrict flow.

 

[milkyway]

Re: What is the Functin of the Manifold?

Tests was done on trailer.<br /><br />I'll check all these hoses per your suggestion. But I need first to put back the manifold nad rise. <br /><br />What do flapper valves look like?. I saw no "flapping" think on the elbow and manifold. Just small and wide holes. I inserted the hose in all holes and water flowed freely. I think I'll show the mani and elbow to the parts dealer for comments.

 

[butlp]

Re: What is the Functin of the Manifold?

Again, I'm no expert on the Mercruiser and I hope I'm not leading you in the wrong direction as there are subtle differences between Merc. & VP.<br />If your motor has them I believe the valves are in the same location and look like the VP except they are rubber covered metal disc's. They are located in the "Y" shaped exhaust tubes that come up vertically from the stern drive. In my case I had to remove all of the rubber exhaust bellows and elbow pipe. If you already have the manifold off then it should be easy to loosen all the hose clamps and pull the bellows off. The flapper valves are held in place by a SS pin that passes through bushings in the "Y" tube and are held in place by the rubber bellows and hose clamps.<br /><br />When you tested the manifold, did any water come out of the exhaust ports i.e. the 4 holes that connect to the head and the exhaust gases go through. This would indicate a crack between the exhaust and the water jacket.<br /><br />If all above is OK I would put it back together and confirm that your sea water pump is OK and the thermostat feeds are not blocked.<br /><br />Finally, you really need to get a work shop manual as all of this would be much clearer.<br /><br />Good luck

 

[butlp]

Re: What is the Functin of the Manifold?

Milkyway,<br />Check out the following:<br /> http://www.mooreperformance.org/Two.html <br />Not only do they make cheaper manifolds if you need them but they have a "cut away" which shows you how the manifold works.

 

[tommays]

Re: What is the Functin of the Manifold?

the flaper should be in your y-pipe right at the top merc calls them exaust shutters<br /><br /> very inportant for keeping water from getting into the motor i would change both about 20 to 25 dollars each<br /><br />if the manifold was hot before it will be hot now 1998 till 2004 = about the life span of a manifold used in saltwater <br /><br />if the starbord side is a littel bit cloged the water will take the easery way out through the port side<br /><br />if the starbord side was compleatly closed it would all come out on port the system does not force water through both manifolds evenly there is only one pump and it will allways takes the easy route<br /><br />tommays

 

[milkyway]

Re: What is the Functin of the Manifold?

""When you tested the manifold, did any water come out of the exhaust ports i.e. the 4 holes that connect to the head and the exhaust gases go through. This would indicate a crack between the exhaust and the water jacket."" >>> NO WATER CAME OUT OF THE EXHAUST PORTS. SO I ASSUME THERE'S NO CRACK INSIDE THE MANIFOLD.<br /><br />THE MANIFOLD AND ELBOW PASSAGES ARE ALL CLEAR.I USED A FUNNEL TO GUIDE THE HOSE WATER IN THE PASSAGES AND TURNED THE HOSE ALLLLLL THE WAY, AND WATER ALL PASSED TO ALL OTHER HOLES AT THE OTHER END AND NO WATER CAME BACK UP WHERE THE FUNNMEL WAS. LOOKS PRETTY GOOD TO ME.<br /><br />IN REMOVING THE OLD GASKET FROM THE MANIFOLD, THE TWO HOLES WERE COVERED ENTIRELY BY GASKET. I MEAN ENTIRELY - THERE WERE ONLY 2 WIDE HOLES THERE. I HAD ONLY 2 HOLES BEFORE CLEAN UP, BUT NOW I HAVE 4 HOLES ON THE MANIFOLD THAT MATCH EXACTLY THE 4 WIDE HOLES ON THE ELBOW. VERY STRANGE. COVERED UP WITH INTENT?<br /><br />WHEN I CHANGED THE SPARK PLUGS LAST MONTH, I NOTICED THAT ONE SPARKPLUG ON THE STARBOARD SIDE SEEMED WET, DARK AND SMELLED LIKE GAS. TONIGHT, I REMOVED THE SAME SPARK PLUG AND IT AGAIN LOOKED DARK, WET AND SMELLED GAS. THE OTHER 3 PLUGS ON THIS SIDE WERE ALL DRY. WHAT IS YOUR DIAGNOSIS OF THIS?<br /><br />THANKS FOR ALL YOUR ADVISE, BUT DON'T GET TIRED OF ME. PLEASE KEEP POSTING ALL YOUR COMMENTS.

 

[tommays]

Re: What is the Functin of the Manifold?

there are many different ways of cooling the motor it depends if anybody has taken it apart before you thats were the service manual for your motor becomes very inportant<br /><br />there are 2 types of gaskets one with 4 holes and one with two and a blocking plate it depends on the system<br /><br />some fresh water cooled motors use raw water in the manifolds and some cool the manfold with the fresh water<br /><br />the ellbow should allways be cooled with raw water<br /><br />i hope you not more mixed up now i think your motor was raw water cooled<br /><br />as far as the plugs marine motors are usally set up on the rich side but until you get the motor running at and even temp it will be had to say<br /><br />tommays

 

[milkyway]

Re: What is the Functin of the Manifold?

Well I finally reinstalled the mnaifold and elbow. What a task it was because of its size and weight and limited working space. The two holes on the manifold are really covered with gasket, as restriction, according to the marine store. So I again have 2 wide holes. I now fully understand how the manifold works, and how raw water cools it. For some unknown reason, the starboard manifold and elbow is cool as the port. Hope this continues. Tomorrow, I will check water flow in all hoses with engine running. I also saw where the flappers. Looked and functioned like ventilation shutters of a bathroom or kitchen cooking exhaust fan.

 

[tommays]

Re: What is the Functin of the Manifold?

well you got it off and on yourself did not break it saved a lot of money and learnd a lot to<br /><br /> <br />that is a great result<br /><br />tommays