Freeze Plugs on Merc Cruiser 5.7 350

My_Dinghys_Dinghy

I am working on my floor of my boat and decided I wanted to hear my engine run. I have nothing in my boat right now so I can see right back to the engine, I HAD WATER POUR OUT OF A FREEZE PLUG and I noticed that the freeze plug was just laying in the engine compartment (Actually before I started even thinking about starting it). Was wondering what it was off of and figured out that it had to be a freeze plug.
Well, low and behold, it's the one UNDER the motor mount on the PORT SIDE closest to the front of the boat (Again, nothing in there right now).
So, questions I have, can I use a rubber expandable one to fix it or does it have to be brass?
How difficult is it to replace or should I just spend a few bucks and make an appointment at the marina?

frenchship

 If that freeze plug pop out it probably that the water inside the engine froze during winter, was your engine winterize ? hope that is the only problem, what ever liquid that was in the engine froze.  Usually does plug just not fall out . As to repair that maybe somebody on this forum would know something about it . Good luck

My_Dinghys_Dinghy

yes, was winterized and then emptied and dried. I am wondering how this happened. Freeze plugs usually 'pop' while under pressure, not while sitting or while even sitting in an engine that has very little, if any, water. It's hard for water to sit in the block when your outdrive is down and water lines are opened and blown out. Plus, where those plugs are located, it would have been a 1 in a 1000 chance (Albeit still a chance but I don't think so) Anyway, I am looking on how to fix it and move on.

Handymans342

There is a sealant applied with freeze plugs I believe and if that one wasnt it may just fall out when it got real cold and shrank

frenchship

When you replace the plug used a brass plug instead of steel which will rust specially in salt water and coat the plug with a shellac sealer. Clean the hole in the block so it has no residue from the old plug. I don't know much about those rubber plugs so maybe somebody else would know.
But that plug should not have come out by itself. I would investigate if it wise mine..... 

checkmate

I had mine come out 2 seasons ago over the winter months. Don't know why, I winterize it the same every winter. I wasn't able to access very easy because the motor mount was in the way. I tried using the rubber/ brass fitting to plug it but I couldn't tighten the bolt down because of the motor mount bracket was in the way( plus I was upside down hang over the engine doing it blind). I ended up wedging and pounded the original back into place. I've had no issues since. I've checked it multiple times to see if it leaks water and it doesn't.

My_Dinghys_Dinghy

Checkmate, did you use any sealant? I know they're compression type when they go in. Mine is under the motor mount HOWEVER, I have my entire interior pulled from the boat as the floor was really weakened over this last winter. I was just getting 'itchy' and glad I did. I can get to it pretty easily but the motor mount being in the way makes it very tricky.

checkmate

To be honest I can't remember. It all happen so quick and I thought my boat was sinking so I was working twice as fast and the marinas mechanic was gone for the day. I thinking yes but can't remember what I used. Sorry. But on a good note that was the only thing wrong and I still can't figure why it happen.

212rowboat

Use permatex aviation gasket sealer on the new plug and you won't have an issue again. Look, blocks expand and contract and those things just get tired... Especially with salt water running over them.

My_Dinghys_Dinghy

I am at the point I need to find someone who has a boom that I can hold the engine in place so I can pull the motor mounts (and also the adjusters without moving their settings). I was going to slide it in place and then use something to pop it in, however, I won't be able to see the whole plug and only have 'touch' to tell me if it's in place, so another little fix to get it to the water.
Thanks RowBoat for the gasket sealer and what to use.

Stodge

I had one pop when I got the engine powered up to get on plane.  When my mechanic looked at it he said it was marked up like it had been put in crooked.