frost plug on stern drive problems

[clearlakeboater]

Hi there, I have a 1973 Larson Lapline with a 120hp mercruiser(alpha one?). Last summer I noticed that the "mercruiser" sticker on the starboard side of the stern was coming off, and that there was what seemed to be water coming out of it. I peeled the sticker off to reveal a frost plug, that was falling out. I winterized the stern the previous fall, and filled it with new oil, and then used the boat for almost two months before this occured, so I am assuming that it didn't freeze, although when I drained the stern that day, it did have water in it. I refilled the stern with new oil, and tapped the frost plug back into the hole, it seemed to be tight. About three weeks later, the frost plug was popped out again, and the stern was full of water again! I don't think that the stern is damaged, but some how it seems to be sucking water in the bottom, pressuring up the case, popping the plug,and pumping the oil out of the hole. Any info would be helpful. Thanks for reading! Chris

 

[clearlakeboater]

Re: frost plug on stern drive problems

Sorry guys, this should have been in the i/o forum. I must be getting sleepy!

 

[WillyBWright]

Re: frost plug on stern drive problems

JB will be happy to move it for you.<br /><br />The frost plug is there to save the upper drive from freeze damage. It apparently wasn't entirely effective at it's job. You'll need to replace it ASAP. I'm sure it's a common SAE size like 3/4" or so. Water pressure is forcing it out now. If it pops out, your motor will starve for cooling water. Not a good thing! Whenever I winterize, I pour antifreeze down the hose that attaches the thru-transom fitting to the thermostat housing. That chases any water left in the drive right out the back.<br /><br />You'll need to find the source for that water. I suspect a crack in the cooling passage of the upper drive housing. If you catch it early, you might be able to just replace the housing. Let it go and you'll be replacing the whole drive.

 

[clearlakeboater]

Re: frost plug on stern drive problems

Thanks Willy, Does this explain where the oil is going? I assume it is out of the frost plug. If the water jacket is cracked, I suppose it would be obvious once you dissasemble the drive? Thanks again, Chris

 

[Fishermark]

Re: frost plug on stern drive problems

I don't believe the plug on the outside / starboard side - the welch plug - is freeze plug per se. I believe it is simply a plug to enable you to get at the pipe plug on the inside. There is no water behind that outer plug. (Or at least there shouldn't be - that area is a pocket where the shift slide goes in.) If I'm wrong, someone will set me straight shortly! For what it is worth, the plug on my Dad's boat has been covered up with JB Weld a long time ago.

 

[Don S]

Re: frost plug on stern drive problems

I posted this on the other thread also:<br /><br />The welch plug (#21) covers a plug (#22) known in the service manual as a "Pipe Plug, water pocket"<br />If you look at the diagram below, you will see it's in the water area of the drive.<br /><br />