Never had this happen before and I've never taken an exhaust manifold on/off. With the engine running there is a slow dripping from what appears to be off the bottom rear of the starboard side manifold. Also a bit ends up on the riser. It is leaking enough to kick on the bilge pump every now and then. Are there freeze plugs in the exhaust manifold? Any ideas on how to tackle this one would be greatly appreciated. If I don't do it myself it will sit in the shop for a month this time of year before anyone will get to it. Engine runs fine with no overheating. No dripping with the engine off.

Check the hose and check valve on the bottom of the manifold. Its been a while since I had mine off but I don't remember freeze plugs in the manifold.

Ran the engine on the hose today leaning over the engine with a mirror. There is what looks like a pipe plug, one at the front and one at the rear that tighten with what looks like close to a 1/2" allen wrench. The rear one on my exhaust manifold is leaking there. I tried a 1/2" ratchet, too big, 3/8" was too small. Anyone know what size those plugs are? Looks like all it needs is to be removed and reinstalled with some thread sealer.

9/16 allen if I remember correctly.

Expensive Date - I'm thinking that it can't be 9/16" allen because 8/16th" would be 1/2" and my 1/2" ratchet was too big.

I just looked in my tool box, my 9/16 allen has brass on it but I'm not sure if I used it to take the plugs out of the old manifolds before I scrapped them or used it to put the new ones in the Imco's. Can you just try putting different size bolts in there (head first) and see which one fits? Now that I think about it there might have been two different sizes, but it was a few years ago and really was not paying attention when I pulled the plugs. The only reason I remember the 9/16 is I did not have one and had to take it off my truck.....benefit of having a tool truck in your driveway.


http://www.mercruiserparts.com/Show_...fold+and+Elbow


Page down this should be what you have, there is a freeze plug and I am pretty sure there is a #2 plug also in the rear.

Ok, think I just remembered that the Mercury ones were 7/16 I don't have one but they are painted black so no brass marks.I probably just put it back on my truck when I was done.I will PM you my cell I can ship you one out of Fresno tomorrow you should have it Wen. if you need it as its an odd size may be hard to find.

Expensive Date - You were correct the first time. The Allen size is 9/16". I took your advice and tried different bolt heads until I found the correct size (simple approach is always the best approach thank you). I'll see if I can find one locally today. If not I'll get in touch with you. Thank you for your generous offer.

I'm waiting for the 9/16" allen head socket to arrive on my doorstep (ordered from Sears). Hopefully this "drip" will have a happy ending and I will just unscrew the plug, clean it up a bit, apply some thread sealer, and retighten the plug.

Thanks Tim for the offer of the tool loan or possible sale and the diagram of the exhaust manifold and related pieces. It is so nice having a "family" of experts who are willing to help out at the drop of the hat.

I gave up waiting for the 9/16" allen wrench after not being able to use my boat for a week. Sears blew past their promised delivery date and could not locate the tool or come up with a valid tracking number (a first for me as Sears is usually spot on).
I tried using a long 9/16" headed bolt and vise grip pliers but the pliers turned on the bolt no matter how hard I clamped down on the bolt. So, I got a 2" treaded bolt with 9/16" head and designed this:



I added two extra nuts and one washer to the mix and my neighbor kindly welded the final nut to the bold. With this tool and a foot long ratchet with a 6-point 9/16" socket I was able to back out the leaking pipe plug in the exhaust manifold.



My neighbor cleaned the pipe plug on his wire brush grinder and I could see no reason not to reinstall it. I coated the brass pipe plug with a high temp anti-seize / thread sealer, again provided by my neighbor who is the U.S. distributor for this product, and reinstalled it using the homemade tool.



I hooked up the hose to the boat's fresh water flushing system fired it up and there was no more dripping. End of story. Someday maybe my 9/16" allen wrench I ordered will arrive. Until then the homemade tool will do just fine. A boat mechanic I called said it was not uncommon for these plugs to be loose on even newly purchased manifolds.