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3.0 OMC Freeze Plug Quandry

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dadbaker172

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OK. New to this forum and hope someone can lend some advice. 89 model OMC Cobra 3.0. Put a new impeller in the foot and almost immediatley pushed out a freeze plug in the back of the block. This was the first time I had it in the water and it was properly winterized last year. Two questions as I am completley ignorant to the finer points of boat repair: First, is this common? I'm concerned that I may have more going on as I can't see a new impeller building enough pressure to push out a plug if eveything else is right. Second, does anyone have the correct part number for the plug that should go back in this boat? NAPA has a brass plug but the shoulder depth is about half of the one that came out and I assume I need plenty of shoulder on the plug to keep it in place. The plug goes directly behind the flywheel and I have the old one recovered once I pulled the engine. It's approx. 2" outside diameter with 1/2" shoulder. Any help would be greatly appreciated. Thanks in advance!
 
dadbaker172 said:
  1. 89 model OMC Cobra 3.0. Put a new impeller in the foot and almost immediatley pushed out a freeze plug in the back of the block.
  2. and it was properly winterized last year.
  3. First, is this common?
  4. I'm concerned that I may have more going on as I can't see a new impeller building enough pressure to push out a plug if eveything else is right.
  5. Second, does anyone have the correct part number for the plug that should go back in this boat? NAPA has a brass plug but the shoulder depth is about half of the one that came out and I assume I need plenty of shoulder on the plug to keep it in place.
  6. The plug goes directly behind the flywheel and I have the old one recovered once I pulled the engine. It's approx. 2" outside diameter with 1/2" shoulder.
Click to expand...


  1. These are casting core plugs... not freeze plugs.
    If one gets pushed out due to freezing, consider yourself fortunate.
  2. If this core plug was pushed out due to freezing, your engine was NOT properly winterized last year.
  3. Not if properly winterized.
  4. Your sea water pump would be incapable of pushing a core plug out.
  5. Mic the ID of the core plug bore and the necessary depth.
    Take these dimensions to NAPA with you.
  6. This core plug should be just forward of the flywheel.
    If I were you, I'd be also looking at all other areas for freeze damage.


I'll suggest that you learn how to winterize this engine, and that you always.... no exceptions...... always probe your engine drain ports with a small tool or wire to clear any rust scale from the ports.


And don't fall for any of the Camco or similar Winterizing kits! <click here to read a review



These are a Bad idea no matter what day of the week and no matter what you had for breakfast!





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actually, for some reason, that particular rear plug on the 3.0 does have a bit of a reputation for just popping out, but as mentioned look for more damage. Crank your head upside down under the manifold port side and look along the block just below the seam of head and block.
Quite a few people with 3.0s have winterized correctly and yet found that rear plug laying in the bilge in the spring. I dunno if it's water in some pocket, or just the warm/cool cycling of the casting letting it loosen over time. I staked mine in when I did the coupler.
 
Yes... I know the name and reason for the orifices to which we refer are officially "casting" ports and plugs however the most common nomenclature would be freeze plugs. I also understand that the reason for their existence has nothing to do with prevention of freeze damage and is solely for removal of casting material from the block when manufactured. Now then. I do very much appreciate the input as I stated am in no way a "boat guy" and if not for my kids I'd never have one. I do however know my way around an internal combustion engine as I have several other toys that go fast. I have looked the block over thoroughly and see no other signs of damage, cracks, stress bulges or weeping. No water residue in the oil and no cracks in any of the risers or manifolds. Thanks for the advice on the winterizing kits. Looks fairly suspect to me. Strange that this plug has the reputation for self removal. Still looking for the plug itself though. Any ideas on a part number for it? Would not want to spend what will apparently be $40 plus on a 3 ounce piece of brass that won't fit and would appreciate any info anyone has. Thanks much!
 
One more note for the boat guys..... In looking more closely at the rear of this engine it appears that this plug had been leaking for some time and the new impeller apparently was enough to push it out. I've got rust trails running down the back of the block just under the plug therefore I have to assume that there has been some amount of water finding it's way by this plug for some time. Just seemed strange.....
 
The shoulder shouldn't make much difference. Just make sure its sealed real good. If it was pushed out? Then something wasn't done right? Who did the winterization? Possible the block didn't drain as good as you thought. Profile,location? Salt/fresh water? There is a rubber seal that can fit in the hole.If it's used in only fresh water it would be ok to use.Salt water not so much. 0311377 OMC part# Boats . net says they have it?(hate boats . net)
 
dadbaker172 said:
Yes... I know the name and reason for the orifices to which we refer are officially "casting" ports and plugs however the most common nomenclature would be freeze plugs. I also understand that the reason for their existence has nothing to do with prevention of freeze damage and is solely for removal of casting material from the block when manufactured.
Click to expand...
I hate to split hairs here.... OH hell... who am I kidding, I love to split hairs. :D

Keep in mind how many years ago we began casting iron for use in engine manufacturing.
Also, we had not yet perfected Ethylene Glycol as an engine coolant.
For the poor sucker who did not drain his engine for a freezing cold spell, his casting core plugs (aka Welch plugs) were pushed out.... and that's if he was lucky.
So this is where the so called common nomenclature came from.

But even back then..... the purpose of the Welch Plugs was NOT for freeze protection.



Call these what you wish..... but I'll always refer to these as casting core plugs or Welch plugs. :D :D





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Had one come out years ago. Autoparts guy provided a replacement (like yours, not as deep on the sides) and a can of some kind of thick varnish. Coated sides and tapped the plug in using a hammer and the biggest socket I had. Plug is still in after 20 some summer seasons of operation.
 
YEA!!!! What Rick said!!! "But even back then..... the purpose of the Welch Plugs was NOT for freeze protection." In some cases they do pop out and "maybe, just maybe" save the block?? But I have seen a case where the plugs were popped out and the block was cracked too."made a real good paycheck on that one"
 
New plug with loctite 271 around the sealing edge will cure most drips, unless the block's surface has deteriorated...perfect seal would be another alternative...
 
Ok boat guys... Thanks for all the info. Found a plug at Napa that worked. Smothered it in gasket varnish and smacked it in with a 3/4 drive socket. Put the exhaust riser back on and ran water through the engine for thirty minutes at about 60 PSI. No leaks and no water in the oil. Now I'm in process of replacing the seal or gasket around the outdrive. I refuse to name it anything as I'm obviously ignorant to the proper names of parts for boats so I will refer to it as the "rubber thingy" that seals against the hull and keeps the lake out of the boat.

At any rate I appreciate the help from all. Once I get the new seal installed and the upper part of the outdrive back on the boat and engine back in I'm ASSUMING that the gimbal and engine alignment (I have a shaft borrowed) is fairly simple and not much differnt than aligning a transmission and differntial housing on a car build. IE: both on the same plane, in phase, etc., etc... so as to prevent vibration and shaft failure??

And for clarity.... How do you guys put up with the expense of these things?? I've spent more on this boat in last two years just keeping it up and fixing picky crap than I PAID for the thing in the first place... And I thought racing motorcycles and cars was an expensive hobby!! LOL
 
Alignment: The motor should go back in the same as it came out.
So alignment should be close and fairly easy.
Just make sure the shaft with grease on the end,
when it comes out the marks need to be even and all the way around the end.
Your lucky your not paying for the "LABOR" too.
If I didn't fix my own??? I'd be going out on head boats???
My new wife(never had a boat or a man who could fix anything)doesn't understand owning a boat.
She thinks the boat club is the way to go.NOT!!! $2000 membership and then $200 month and then you still pay for gas.
The only benefit is you don't have to clean after your done. She thinks it's a great idea.
 
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