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Exhaust Manifold water drain plug

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Captain Quint

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I have a 1996 Mercruiser 454, both drain plugs on the exhaust manifold, port and starboard, are plastic. They have become brittle and upon removing them to replace them with metal ones, have broken off leaving about half of the threaded portion in the threads of the manifold. I have tried various extraction tools without success. Do these drain plugs melt, or does the pipe dope harden over time with heat? Is there some kind of solvent that will help loosen the threads? Any help in removing what is left of the threads in the manifold is greatly appreciated.
 
There are no brass plugs that replace the blue ones. Gently install them with grease and never over tighten and make sure the O ring is on the plug.
Now, heat up a small flatblade screwdriver, insert into the broken threads, let cool ,remove threads
 
Captain Q - I replace the blue plugs every 2 -4 years when I winterize, and grease them like BT Doc says.
 
I had the same problem once. Tried easy outs and screw drivers. All that did was put a hole in the broken plug and pressed the plastic into the threads. To get the threads cleaned I made my own thread chaser using a 1.5" bolt of the same threads and threaded a nut on it. I put it in a vise and cut 3 cross slots in the end 3/8" deep. I then started to thread it into the drain holes carefully using a shallow socket and 3/8" drive. The plastic stuck in each hole came out in the cut openings of the bolt. I used Mercury 2-4-C grease on the new plugs and carefully installed them.
 
Can you explain this sentence a little more...we are confused..."I put it in a vise and cut 3 cross slots in the end 3/8" deep. I then started to thread it into the drain holes carefully using a shallow socket and 3/8" drive. The plastic stuck in each hole came out in the cut openings of the bolt."
 
He just made a thread chaser out of a properly sized bolt...you can get the same effect by cutting two slots into the bolt's threads radially....a cutoff wheel works well...
 
The 1st time I ran into this issue, ( Volvo Penta), I got lucky, a flat blade screw driver jammed into the plug removed it.
I bought a brass insert that screws into the block, with the other end threaded to accept the blue plugs. Now if, (when), one breaks, it’s easy to remove the brass unit & deal with it on the bench.
The blue plugs are handy for winterizing, as they are tool-less, & can be easily undone with the boat stern down on our steep boat ramp, after fogging at the dock.
The dealers don’t give those plugs away, I’m thinking of brazing a small bit onto a brass plug, to make a “T” shaped brass plug, & never deal with those plastic ones again.
Makos explanation is simply the way to make a po-boys tap. It wouldn’t be as strong as grinding 3 grooves into a bolt, but you’re only dealing with plastic, (Teflon), so it’s fine. If you elect to make one, I’d turn a nut all the way down the bolt before you grind a groove. When you remove it, it will clean up the threads.
If you have a tap/die set, you probably have the tool required.
Notice the grooves on the taps, they allow the cuttings to be removed from the bore, which is what slicing into a bolt does.
 

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The Blue plugs thread into a metal adapter that threads into the manifold. Remove it. The "native" hole in the manifold is
a standard size and you can find a brass plug to thread into it.
 
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