Seawater Drain Plugs on Merc 3.0L

darius

Recruit
Joined
Jul 31, 2010
Messages
4
I'm winterizing my '99 Merc 3.0L w/Alpha 1 for the first time. I do not have the original owners manual for direction on how best to drain the seawater from it and would appreciate some advice to make sure its done right. I have located the plug on the bottom of the exhaust manifold as well as the one below it on the side of the block. Also disconnected the hoses at the water pump. Some references I find say there is another plug on the block, but if there is one I cannot see it. Any advice from a seasoned veteran familiar with this engine would be appreciated.

Also finding conflicting advice on whether to simply pull the plugs and drain the seawater or drain and refill with the pink antifreeze. Is it necessary, and if so which hole do I dump the pink stuff in?

Thanks
 

antsmands

Seaman
Joined
Apr 24, 2007
Messages
58
Re: Seawater Drain Plugs on Merc 3.0L

Hello Darius;

I have a 86 Merc but I believe the drain plugs are the same. As you mentioned there is one on the exhaust elbow and on the block. I drained the water from each and filled the exhaust elbow and the block with RV antifreeze. You should pour both until the "pink stuff" comes out of the drain plug, close the plug and fill until full. You can best fill the block by removing the thermostat housing and filling from there untill it is full. The RV antifreeze is safe to -50F and has rust inhibitors. I have heard you can winterize without antifreeze but the leftover moisture in the system will promote rust.

Hope this helps;

antsmands
 

antsmands

Seaman
Joined
Apr 24, 2007
Messages
58
Re: Seawater Drain Plugs on Merc 3.0L

Hello Darius;

I have a 86 Merc but I believe the drain plugs are the same. As you mentioned there is one on the exhaust elbow and on the block. I drained the water from each and filled the exhaust elbow and the block with RV antifreeze. You should pour both until the "pink stuff" comes out of the drain plug, close the plug and fill until full. You can best fill the block by removing the thermostat housing and filling from there untill it is full. The RV antifreeze is safe to -50F and has rust inhibitors. I have heard you can winterize without antifreeze but the leftover moisture in the system will promote rust.

Hope this helps;

antsmands

PS Be sure to also clean the drain holes in the out drive and drain it also. Keep it in the down position until spring to limit stress on the transom.
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Re: Seawater Drain Plugs on Merc 3.0L

I am pretty sure you got them all. That is all I do on my 2.5l (very very similar). I am on my 4th year of just draining and leaving it on an '83 boat. I believe the previous owner did the same. Never had an issue and I know for sure mine will not freeze in any weather on this planet with just air in it.
 
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