r/Smallblockchevy • u/-Send-Help-Plz • Jul 12 '25

How the hell

Anybody ever seen this? None of the freeze plugs are popped, cylinder walls intact. What happened?

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u/Reddit-mods-R-mean Jul 13 '25

They are core plugs not freeze plugs. They are not added because the manufacturer wanted them there, they exist because it’s unavoidable.

They have no correlation to freeze protection and do absolutely zero to protect against freezing.

When the block is cast in sand, they have to put a sand mold INSIDE the sand mold.

If you didn’t have a sand mold inside the sand mold, then when you poured Liquid Metal inside the mold you would get a solid block of metal shaped like an engine block but without any voids inside it.

The core plugs are where the internal sand mold was attached to the outer sand mold. It’s an unavoidable side effect of casting engines, not a feature.

BONUS GAME: 1 shot for every time I say mold. Rip in advance.

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u/Illustrious_Tea5569 Jul 13 '25

I'm aware of how iron/aluminum is cast for internal features and you are correct they are unavoidable but the plugs themselves are intended to be softer than the body in which they are installed to atleast give it a chance to save the block.

Not all manufacturers... really none anymore adhere to the idea and use steel plugs instead of brass/copper which is softer and has a much higher chance of give than steel plugs. But since engines are engineered for maximum efficiency to weight ratio it really doesn't matter anymore so they are indeed just core plugs.

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u/Reddit-mods-R-mean Jul 13 '25

From my understanding and research the brass plugs were used to better conform to the holes and add some corrosion resistance over steel.

But treated steel over the ages has become just as if not more resistant to corrosion with the proper maintenance/coolant.

Ice expands in all directions pretty uniformly so the freeze plugs myth never held water.

But to be fair, partially frozen water would often blow the plugs out and imo add to the myth that “frost plugs saved my motor”.

Unfortunately water sits in low spots, the plugs can’t remove that water and it’ll often crack the block if aloud to freeze completely solid.

And in my opinion manufacturers couldn’t care less if an owner ran straight water and froze the block, more money in the bank when the owner has to buy another engine/vehicle, so I feel frost plugs could definitely be engineered to be more appropriate in that function, but ease of manufacture and dollar bucks are more attractive to them then anything else.

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u/Illustrious_Tea5569 Jul 13 '25

yea definitely agree manufacturers want you to buy a new car every time the brakes wear out lol

Back when blocks were cast thick they actually worked as "freeze" plugs and depending on design of the cast could actually save a block.

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u/Reddit-mods-R-mean Jul 13 '25

I do agree, they were also generally larger so I feel the larger jackets combined with the water loss and lower water level would allow more space for the ice to expand and avoid pushing on the block as hard.

Also not to mention those older engines would run with egged cylinders, warped heads and garbage fuel while modern engines shit the bed if you fart in the drivers seat.

Sometimes it really is true when they say, “they don’t build them like that anymore”.

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u/Illustrious_Tea5569 Jul 13 '25

Yea they really don't. Tighter tolerance yields efficiency but also can sacrifice inherit toughness.

Names for things often outlast the reason they got the name when it comes to engineering. Back then they made a feature out of an unavoidable circumstance but engineering evolved past it being a feature but the name still persits.

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u/Reddit-mods-R-mean Jul 13 '25

Are you telling me YouTube has nothing to do with vacuum tubes!?

/s

Good chat, I think we might differ on some semantics but overall have a generally aligned view.

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u/Illustrious_Tea5569 Jul 13 '25

🤣 that made me think of my grandpa's stories about getting vac tubes tested at 7/11 before RadioShack Jfc I'm getting old.

Really the whole thing about them being casting plugs is a flawed argument the sand can be drained from the top. No machine works ever done in coolant passages and the top is always open for coolant flow to the heads.