The truth about so-called "Freeze-out" plugs
 

This has come up a few times at work. I hear people mentioning freeze-out plugs, and every time I ask what they're for, people tell me that they're there to prevent damage if the coolant freezes. At this point I always stop and correct them. Freeze protection is a nice side-effect, but what they're really for is to make it easier to wash out the casting sand during manufacturing.

Just a little fun fact. If anyone has any more fun (or not particularly fun) facts along these lines, share 'em.

Thanks, ya learn something new every day...

I found this out a few years back when I was trying to figue out why the freeze-plugs didn't pop out on my Nissan pickup when it froze.

they are supposed to protect the block from cracking if the coolant freezes but they usually are so rusted in that the block cracks anyway...The hole is there for the casting process but the plug is for the freeze protection as well as to plug the hole.

The plug is only there to plug the hole. I've never seen a block, even a clean one, freeze out the plugs instead of cracking.

Just because you haven't seen it doesn't mean it doesn't exist/happen...I've seen freeze out plugs pop out during a freeze and actually protect the block. Granted the engine shouldn't have had water in it during the winter time but that's another story.

I have also seen freeze plugs do the job and save the block from cracking.

I've never heard of that happening and always thought they were there to ease cleaning. besides, if mine ever popped out, it would probably be easier to replace the engine than to pop them back in :)

I've never had to worry about freezing, to damn hot here. Our winter = 50 degrees.
The only problem that we ever have is the plugs drying out from the heat.

Generally if a core plug does pop out it is more luck than anything, many blocks have cracked since the plugs didnt pop out. On a side note, most race engine builders at the higher levels of racing (Nextel Cup, etc) tap the core holes and use threaded plugs that can't pop out.

Quite a few people, even technical professionals, seem to think that if water is moving it won't freeze. For example, the practice of letting water run at the end of a pipeline to prevent freezing is not based on the water moving, but rather that the near freezing water is expelled while warmer resupply water brings enough heat into the system to offset heat loss.

PS: where I work we manufacture freeze protection bleeder/drain valves so I deal with this issue often. Most locomotives in the U.S. and Canada have one of our valves on the engine block to protect it from freezing since they do not use antifreeze in locomotives ...antifreeze results in reduced heat rejection and therefore reduced power and even a couple percent = lots of $$$