How do you change a core plug?

Answer 1

Core plugs are fitted in the round holes along the engine block. They are erroneously referred to as "freeze" plugs. Somewhere along the line someone got everyone to believe these plugs would pop out if the water in the block froze. Instead, 99 times out of 100 they wouldn't and the block would crack. Core plugs are inserted because engine blocks are molded using sand. The holes let the sand out and then those channels act as coolant passages. The plugs are solely to plug the holes and offer no freeze protection.

Changing them is quite fiddly at least when the engine is in the car. The biggest problem is finding room for your hands and tools.

To remove a core plug take a punch and a hammer, and knock on one side of the core plug, until it turns in the hole. Then grab hold of the other side with a pair of pliers. Twist and pull to get it out. Be extremely careful not to knock the plug into the engine block. You might not get it back out, and it might get stuck in such away that you won't get a new core plug in. You might want to bore a hole in the plug, so you can grab the plug with pliers or pry it loose with a screwdriver through the hole.

To install a new core plug, get a socket that fits exactly inside the plug (which might be hard to find) and use an extension and a hammer, to drive it back in the hole. Take extreme care to make sure the plug is driven straight into the engine block. If it's not straight a leak will occur.

Estimated time for installing a core plug for the first time is one hour, in addition to remounting parts and refilling antifreeze.

If you're installing an engine heater, read the heaters installation instructions. Different heaters will not fit in all core plug holes. You may need to remove a specific plug.

If you go ahead and to this, remember: You might render your engine useless or in need of major repairs, and it's not my responsibility.

A last note: I did this on a Volvo 245. They have very large engine rooms with loads of workspace, and yet I had trouble finding enough space for my tools (especially the socket and room to swing the hammer hard enough). I will think twice before doing it again. The only pleasant part of the job is the price of the core plugs, at only 4 dollars.