[austin_colby]

I just replaced the impeller on my '78 Merc 700 and the water jacket cover seems to be leaking around all three spark plugs. It never did this before the new impeller but I noticed quite a bit more water pressure from the pee hole now. After reading about 20 or so posts about this common problem, I have come to the conclusion that I would like to either a) put some marine quality high temp silicone around the cover or b) just leave it alone. It doesn't appear to affect anything and the motor runs just fine, just a drip here and there from the cowling cover. Any advice would be appreciated.

-Austin

[Yepblaze]

You are correct in assuming it can be let leak without much problem. (other than erosion making it worse after time.

I have in the past, cleaned around base of spark plug real good with wire brush and solvent with plug in place.

Blow dry.

Then remove plugs, (usually use new ones at this point).

Take the plug and with washer in place squeeze out a 1/8" bead around the threads just below the washer.

Now the hard part, WAIT a few minutes for the silicone goop to start to skin over. About 3-5 minutes on a warm day in the shade.

Then screw in plugs, the silicone should goosh out into the clean cavity and seal it up. Wait a few hours before using it to let the goo dry.

[Texasmark]

You answered your own question. Yes your pressure is now higher resulting in the discovery of a leaking water jacket cover, probably due to corrosion at the gasket/cover interface....common problem.

No it hurts nothing at this point if you don't mind a little water residue. Over time, if it continues to leak it will get worse, because corrosion will get worse and one day you'll have to change the gasket......really quite simple.....as long as your screws cooperate and come out like they are supposed to.

Since others seem to have a successful repair with silicon go for it. What the heck.

Mark

[Plainsman]

I learned the hard way and insisted on changing the seal. I broke something like 10 bolts and it cost over $200 to get them out.

Use the marine grade sealant to stop the leak.