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View Full Version : 1981 S&S, 351 Freeze Plug/Core Plug Trouble


tex599
03-25-2012, 10:10 PM
Went to un-winterize the boat yesterday and noticed one of the freeze/core plugs is missing. It is the one right behind the starter. I think I drained all the water out, we did not have a hard winter here in DFW, so not sure if anything would have frozen to cause this. This is a 1981 with the 351, so it is old with some surface rust. Hoping the plug just rusted. Anyways, can I replace it with the rubber plug or should I remove starter and bang in a new steel one? Are the rubber plugs made to stay in or only a temp fix?

CantRepeat
03-25-2012, 10:44 PM
The issue with just draining the motor is that it sits on an angle. If you look at how the motor sits and where the drain is on the starter side of the engine you will see that if you just drain the block you will still have water in the lower part of the block.

I had the same thing happen to me on my 92. It push out the freeze plug behind the starter. I do not believe we had very cold winter that year. I would guess in the high teens a few nights. I ended up just putting in a rubber freeze plug but from that time on I always put anti freeze in the boat and always put a drop light in the bilge when it was going below freezing.

1redTA
03-25-2012, 11:05 PM
I wouldn't do a steel plug, you can get brass

Jerseydave
03-26-2012, 08:07 AM
I wouldn't do a steel plug, you can get brass

^^ The only way to go. If you install a rubber plug and water freezes in your block again the rubber plug will not pop out. You will crack the block instead.

This is why when I winterize I drain and then refill the engine with A/F.

tex599
03-26-2012, 09:47 AM
Thanks for the info guys. Hope I did not damage anything. A/F from now on. I will pull the starter and pop a brass plug in there. It is real rusty around the hole, so I was hoping it rusted out. But makes sense that there was still water in the block due to the angle.

tex599
03-26-2012, 02:30 PM
Got lucky I think. Put in the rubber core plug and took it down to the water, started up and let run for about 15 minutes, up to about 160F. No external leaks and the oil looks good. So no damage if this plug was pushed out by freezing water.

CantRepeat
03-26-2012, 02:38 PM
^^ The only way to go. If you install a rubber plug and water freezes in your block again the rubber plug will not pop out. You will crack the block instead.

This is why when I winterize I drain and then refill the engine with A/F.

I've never seen or heard about this happening. The rubber will surely get pushed out before the block cracks.

tex599
03-26-2012, 02:49 PM
So are you saying i can leave the rubber plug in, as opposed to a brass one? It seems some have never had problems with the rubber and others who say you should replace with brass. I don't think the raw water cooled motors get too hot and the pressure is very low, I might just try leaving the rubber plug in this season. Just check it periodically for leaks.

CantRepeat
03-26-2012, 04:28 PM
So are you saying i can leave the rubber plug in, as opposed to a brass one? It seems some have never had problems with the rubber and others who say you should replace with brass. I don't think the raw water cooled motors get too hot and the pressure is very low, I might just try leaving the rubber plug in this season. Just check it periodically for leaks.

Used a rubber one for 6 or 7 years without issue. I would have needed to pull the engine up to get an angle that would allow me to reinstall a brass plug.

1redTA
03-26-2012, 05:43 PM
[QUOTE=CantRepeat;825386]Used a rubber one for 6 or 7 years without issue. QUOTE]

HeHeHe I would never use a rubber twice

As far as the rubber bung, I used one in North TN for a couple years with no issues in my pickup