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AQ120b exhuast manifold

D

ddutton

Contributing Member
Here are the symptoms. Under power water was coming out of the raw water strainer lid. After taking it in and running on the muffs got worse and I noticed the neck at the top of the drive had corroded through. I have a new neck and gasket but I still think the manifold may be corroded and blocked. A new one is $510.00. I heard about boiling and descaling the manifold. I assume boiling removes salt deposits and is as simple as putting it in a pot and boiling it. Will descaling it removing rust? How is it done.
 
re: "Under power water was coming out of the raw water strainer lid."
In every marine application I've seen, the raw water strainer is on the INTAKE side of the raw water pump and therefore always under suction. IF water is coming out of the top of the strainer while running, you likely have the strainer on the output (high pressure side of the pump) and you have two problems...1) leaking gasket or cracked lid if its plastic., 2) strainer incorrectly plumbed.

re: "the neck at the top of the drive had corroded through"
Stop... do not pass "GO". Fix this. likely most common (after pump impeller failure) cause of engine overheating.... also another cause of engine overheating is a vacuum leak on the lid of the raw water strainer.
Did someone replumb the raw water strainer to get rid of a stubborn vacuum leak on the raw water strainer?

re: " Salt deposits".... There is a product called "Salt-a-way", that when run through an engine while its running, will remove salt deposits. Not a perfect fix it all the time kind of thing, but works often. The on the cheap boiling in a pot solution is white vinegar. Does not really remove rust, unless its loose already.
 
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The raw water pump is before the strainer. Do the exhaust manifolds need regular replacement like the neck? I've used salt away in the past but will give it a good soak and try before I pull the manifold.
 
Yes, the plastic body strainer (SEQ #12) is downstream of the seawater pump on the AQ 120B and other OHC 4's.
This plastic component can become fractured, and does require occasional replacement.

The water neck fitting is also a routine replacement item. (the neck rises out of the water when up on step)
If she won't cool correctly on the garden hose/muffs, she won't cool in the water.

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As for the exhaust manifold..... I'd remove it, and give it a water supply.
Look to see how easily the water exits the rear area.

While these are 1 pc manifold, they still have a mixing chamber within this rear area.
If the ports to the chamber are rust scale restricted, you'll see some abnormal resistance to your water supply.




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Do not underestimate the power of that little elbow. Runs nice and cool on the muffs just need to test it on the water under load for leaks. Thanks guys.
 
Just another reason I scratch my head at swedish engineering!

That was the same symptoms I had before changing out my exhaust manifold. Water pouring out of the strainer lid no matter how tight I tried to twist it on. You can boil the manifold out but if there is excess corrosion on the outlet you might just go ahead and get a new one. Or you might get lucky and find a good used one from a freshwater boat. Here is a less expensive version than OEM:
http://www.marineparts.com/c-458-os...40-b20-23-and-25-liter-855387-7-834438-4.aspx
 
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