Another fun thing about running straight water is that if you have a cast iron engine it will "shed" rust like nobody's business and that will pile up in the bottom of your radiator. I bought a parts car like that once. Radiator was amazingly packed with rust but the core plugs were what stopped them from driving it. One popped and I was able to poke my finger through four more. Ended up scrapping that 5.0. It was so corroded internally I just let it go.

I've asked for brass core plugs at two local chain parts stores and had them look at me like I head two heads. I gave up. Buy mine online and never less than a half dozen. I'll use steel oil passage and cam plugs though.

 

My point was that antifreeze has some anti-corrosion chemicals in it. I have bought parts from the southwest and it's like "oh, it won't freeze here so just use water". Yeah, them here you go, rusted out freeze plugs,

 

Reminder to you folks who think it will never freeze out there in to southwest. There are other GOOD reasons to use antifreeze so this type of corrosion does not happen.

 

They're only called "freeze plugs". What they REALLY are is "core plugs" to stop up the hole left behind where the sand was removed from the casting that allowed space for the water jacket. While coolant freezing MAY cause a plug to "pop" that's not always the case as can be attested to many folks who have blocks and heads with cracks....

 

I recently saw a YouTube video where a guy was replacing freeze plugs. He checked their diameter with a dial caliper and found varying sizes of the same part number. Might want to get a few extras and check them all.

 

Well, Henry Ford did................ That is how cheap you have to be.

 

How cheap can you be to use a steel freeze plug instead of a brass one? Other than plugging off an oil galley, there's no way in the world I'd ever use a steel freeze plug.

 

Do check with a mirror the other freeze plugs on the back of the heads.

 

Replace with brass plugs and your grandchildren might need to attend to them.

 

Got an O'Reilly's handy? https://www.oreillyauto.com/detail/c/pioneer-inc/pioneer-inc-expansion-plug/pio0/epc30b10

a. Drain the radiator.
b. Drill/Punch (with an Awl) a suitable hole in the center and insert a large self-tapping screw and pry the old expansion plug out. If it's really rotten just poke a big hole with a screwdriver and pry it out.
c. Clean the sealing surface in the head with some fine Crocus cloth to remove any corrosion.
d. Apply a thin smear of Permatex Aviation Form-A-Gasket all around the outside edge of the new expansion plug and drive into the head using a deep-well socket that will fit snugly in the recess. Insert until you can see the bevel as shown in your photo.
e. Refill the radiator, etc.

Note that if that's a rusty pinhole leaking that you may want to check all the other expansion plugs for "integrity"... there are plug on EACH end of the heads and 3 on each side of the lower engine block.

 

I've never replaced one, but I would think you should be able to pop that freeze plug out and install a new one pretty easily.