One of the final things in my engine rebuild process is replacing the freeze plugs. We were waiting until the heads and intake manifold were on before doing this. What are freeze plugs you ask? Also known as core plugs or expansion plugs, they’re metal cups (usually made of bronze) that fill casting holes within an engine block. When engines are cast, the cavities are generally filled with sand, and once casting is finished the sand needs a way out…which is where the holes that the freeze plugs block come in. Some people say they’re called “freeze” plugs because they’ll pop out when a freeze occurs, thereby preventing your engine from cracking – while possible, it’s highly doubtful they’re intended to work that way. Most often the water/coolant passage is on the other side of freeze plugs, and over time they can wear out and leak. A cheap, inexpensive part…it makes sense to change these during an engine rebuild. Follow along in the process, there’s even a video!

Follow along in the video, or continue reading, to see the process of removing and replacing freeze plugs. When ya finish, leave a comment and let me know what you think – but first things first…

Removing the Plugs…

This process is pretty simple, you just want to be careful not to push the freeze plug back into the coolant passage in the process of trying to remove it. To help in doing that, a dowel is positioned at an angle – then hammered until the plug breaks free and pivots. From there you can grab the plug with pliers and pull it out from the engine block.

As you can see there are a few that got punched through, which is okay, just be careful that the hole doesn’t get too big or your tool doesn’t poke through and cause you to hammer on something else. I tried using a screwdriver removing my first plug, resulting in the big hole you see above…ya live, ya learn.

After all six of my Small Block Chevy’s freeze plugs were out of the block, it was time to give the water passage a blow out. I waited until now to do this, because I didn’t want residue from this passage blowing out and into combustion or oil cavities in my engine.

The exhaust holes and any other additional holes were taped over before grabbing the air hose.

Then I just worked from one end of the block to the other, blowing pressured air through the freeze plug holes, pushing bits of rust and residue out – making my engine’s water passage as nice and clean as possible…every little bit helps.

How to Replace Freeze Plugs

After that was done I grabbed my new set of plugs and a few tools to button this puppy up! This can be done without a special tool, but there is a special freeze plug tool which I had access to thanks to my mechanic husband (if you’re doing this at home check an auto store…they loan a number of seldom-used tools like this). The tool is designed to evenly apply pressure around all edges of the plug while you hammer it in – it also keeps you from over-inserting the freeze plug to your engine block. While the tool comes with a metal arm, that just makes it more difficult and is only needed when you need to reach down through a crowded engine to insert freeze plugs – we used a heavy-duty socket instead, placing it over the plug tool then hammering until the plug pops into it’s proper spot.

I put a dab of transmission oil around the edge of the plugs to help them slip into their spots. Some plugs went really easily, as you see in the video, and others I had to try at two or three times. Give the video above a watch to see this process in action. These new plugs were a quick, inexpensive thing I could do to help ensure my first engine rebuild is top-notch and stays leak free for miles to come!