Clogged Exhaust Manifold

firstpft

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Jul 6, 2017
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The water ports of my raw water exhaust manifold are clogged with a thick, pasty grease material that only lets water trickle through. The ports are not clogged with rust. I've tried carburetor cleaner, Prestone radiator flush, sulfuric acid, lye, Dawn and CLR. Only the CLR seemed to help a little but the flow is still minimal. I looked for a radiator shop in my area but none have the equipment to clean out the manifold. The ports are too small and twisting to use any type of snake. Other than replacing the manifold, any ideas?
 

Bondo

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exhaust manifold are clogged with a thick, pasty grease material

Ayuh,..... Welcome Aboard,..... What is it, 'n where did it come from,..??
 

firstpft

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Jul 6, 2017
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This is a chevy 305 block inboard in a 24' Penn Yan Tunnel Drive. Not sure what brand it is as it is not the original engine and it looks like they added parts from different motors. When replacing the main engine pulley, the part # was from a Volvo Penta but when I ran the #s on the risers they came up as Mercruiser. I have no idea what this stuff is that is clogging the water ports or how it got in there and it is only in the starboard exhaust. When I got some of it on my hand, had a very hard time washing it off. Finally tried some Go-Jo and that worked.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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May have been manifolds pulled from an oil fouled boat ( from something like the deep water horizon spill ). If the manifolds are oil fouled, you may simply need to replace them.
 

firstpft

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The raw water inlet side of the manifold had a 90 degree threaded brass elbow on it which was preventing me from getting anything mechanical into the exhaust to clean it out. The elbow would not budge when I put a wrench on it and I feared it would snap off if I forced it. A friend of mine suggested heating it with a torch to expand and contract the metal. BINGO! I was able to remove the elbow without it snapping off. I was then able to use a pressure cleaner in the opening and the gunk came flying out in clumps. What the gunk is, I have no idea but water is now flowing freely through the manifold. As a side note, when I got this gunk on my hands, the only thing that would wash it off was Prestone Windshield Washer Bug Remover. (Yes, I was getting desperate) I don't know what they put in Prestone but it worked when nothing else would.
 

alldodge

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Easiest way to remove an oil base product is with another oil base product. You can use motor oil to remove grease, I use diesel to remove most stuff, then wash with soap afterwards

That said, my guess is your just going to need to replace the exhaust
 

HT32BSX115

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Dec 8, 2005
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the only thing that would wash it off was Prestone Windshield Washer Bug Remover. (Yes, I was getting desperate) I don't know what they put in Prestone but it worked when nothing else would.
Most windshield washer fluids are alcohol (Methyl Alcohol) based.

It's possible you (or a previous owner etc) drove through something that clogged the manifolds......(at ambient water temp most "stuff" doesn't clog.......heat it to engine temp, and it coagulates!!)

I would be wondering if the block and heads have the same "gunk" in them......

//
 

firstpft

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Jul 6, 2017
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Thanks for the input. I tried carburetor cleaner (usually alcohol based) but it didn't help. I was also concerned about the block and heads but the water seemed to flow freely to the exhaust manifold which is at the end of the cooling system so I thing that at least the block is clear. The serial number on the block indicates that it was cast between 1980 and 1985 so it is a fairly old motor and I don't know how long it was operated in salt water. When I bought the boat, I full expected to put a new engine in it but since the existing engine fired up fairly easily, some friends talked me into tinkering with it. I will tinker with it as long as I don't have to spend a lot of money on parts like new manifolds at $250 each. Would rather put the money towards a new engine. So until I run into a problem that will cost big bucks to fix, I will continue to enjoy tinkering with this old engine and getting some interesting advise on this forum. :).
 

HT32BSX115

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Dec 8, 2005
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10,083
Would rather put the money towards a new engine. So until I run into a problem that will cost big bucks to fix,

A new engine should include new manifolds.

Old manifolds (especially "Salt" manifolds more than a few years old) are in general ticking time bombs.

When they crack or start leaking, they can destroy an engine if you don't discover it within a few short days....
 
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