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Discussion Starter #1
So I have a 65 mustang with a 289 and the freeze plugs on the front side of the cylinder heads went out and leaked. Now these plugs are brass and about 5/8” deep, which I’m sure didn’t come on the engine stock. I figured I might as well just replace both of the front ones. I went to about every auto parts store in a 50 mile radius and no one had these plugs. So it got me thinking, how deep are the ones on my dads car(he has a 66/289 as well)? His are shallower, we both have the same heads, so what’s the difference between the deeper and shallower freeze plugs? And if I can’t find the deep ones, can I use shallower ones? Will that effect my engine if I have deep ones in the back of the heads and shallow ones in the front? They are 1 1/2” wide plugs btw. Please send help
 

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Deep or shallow depends on the manufacturer. Many aftermarket, and all marine core plugs are brass.
Here's a Mercruiser set-
 

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I like the deeper ones, and that's what I used on my 289 when I rebuilt it. The listing showed they were for a Ford 390.
 

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Discussion Starter #4
Is it ok to use shallow ones in the front and deep in the back? Will that make a difference with anything? Does it really even matter that much?
 

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Is it ok to use shallow ones in the front and deep in the back? Will that make a difference with anything? Does it really even matter that much?
It doesn't matter at all. I like the peace of mind from using the brass ones, but they don't actually do anything. These holes are left by the casting process, and have no function on an assembled engine, other than to not leak.
 

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Yes I do, I like to wipe some Permatex on the plug and the hole before assembly.
 

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I like to use the hardening type of Permatex., not RTV. It's dark brown and has a pretty strong smell. I know it's old fashioned and may be a little harder to find.
 

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In my experience, the deeper ones are less likely to leak or pop out. They are also a little more (but not much) difficult to install. I have had the short ones pop out after a rebuild and no longer use them.
 

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Shellac.

I've had RTV leak with some regularity.

I use deeper ones when I can, the shallow ones seem to get all cockeyed easily. One thing to consider is deeper plugs on the side of the block can be a little tricky to remove down the line. Too long to tweak to the side and if you hammer them in, they can hit the cylinder wall in the cooling jacket depending on the engine... Then fun things like denting the cylinder wall from the inside of the block can happen. Just something to consider.
 
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I like to use the hardening type of Permatex., not RTV. It's dark brown and has a pretty strong smell. I know it's old fashioned and may be a little harder to find.
Worth the effort. I don't like the silicone types at all. This is on the Advance Auto page-
 

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I use the form a gasket around the perimeter of freeze plug. I also suggest you use some sandpaper to clean up the hole prior to install.
 
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