Water leaking from around the top spark plug!

[waterinthefuel]

I see this is quite common but I'm a little worried. It's a 1979 Merc 70 3 cyl. Runs fine before this happened, but now its missing badly. When I went to change out the plugs the one plug that is leaking was much colder, even cool, when the other plugs were definitely warm. I replaced the plugs and within seconds of it starting a tiny drop of water starts to form around the plug, and then it starts to drip. Some are saying water jacket gasket, some are saying the block is cracked.

Anyone have any ideas what it could be?

PS. I did use the search and did find *almost* enough information to not need to make another thread on this but I am worried. A cracked block? I know that a few years ago it got overheated when the water pump stopped working. We fixed it and its been fine ever since with very good compression on all cylinders. I just don't know what's wrong.

Also, whats the secret for getting off the water jacket head bolts and what is the correct torque to put them back on? Also, can RTB gasket stuff be used or should only a replacement gasket be used?

 

[Faztbullet]

Re: Water leaking from around the top spark plug!

What you want to do first is a compression check, if all is ok soak the water jacket bolts/nuts with good soaking lube and replace the water jacket gasket. Use only aviation sealer on the gasket on reinstalling and I have only seen several blocks cracked in 30+years of repairing motors

 

[waterinthefuel]

Re: Water leaking from around the top spark plug!

We replaced the water jacket gasket and the leak is gone. Total cost: $7.00. We changed it ourselves.

 

[ajgraz]

Re: Water leaking from around the top spark plug!

This fix is on the list for my 1979 70hp 3cyl Merc, too. Where'd you get the gasket, and what was the part number?

And if your bolts were rusty, how'd you get them out?

 

[waterinthefuel]

Re: Water leaking from around the top spark plug!

I don't know the part number and the bolts weren't hard at all to get out. We threw away the package. This engine was only run in fresh water since new so it was easy. Just call your local Mercury dealer, he can find it for you.

You have to unlatch the flywheel cover and it tilts rearward and then take off the one bolt at the bottom holding the cowling cover thing and grounding cable that fits over the powerhead. At that point just take the bolts right out! Be careful though. They can strip. Torque them to no more than 8 ft lbs.