how to replace core plugs

12 Steps on How to Replace Core Plugs

Core plugs are thin metal cups that fill the core hole cavities left in the engine due to the engine casting process. The core holes on an engine facilitate the formation of internal cavities for coolant passage inside the engine block. As sand is used in the casting process and the core holes also help in the removal of the sand from the engine block after the casting is complete. The core plugs prevent the coolant from leaking out of the engine, but over time these plugs can corrode and, as a result, cause the coolant to leak. This article will teach you how to replace core plugs of your car’s engine.

Removing old core plugs and replacing them with newer ones may seem a little complicated at first, but with the right tools, you can get the job easily done.

Reasons for Core Plug Replacement

Two possible reasons for core plug failures are corrosion and displacement due to coolant freezing.


Core plugs made of steel can rust over time due to being in constant contact with the coolant mixture. The corrosion from rust can cause the core plugs to leak. If left unchecked, the coolant might get drained out completely and cause the engine to heat up.


Core plugs can pop out as a result of the coolant freezing. As the water and coolant mixture expands upon freezing, the pressure inside the engine block creates expansion, pushing the core plugs out. If the core plugs are unable to stand the pressure, they can pop out, causing all the coolant from inside to leak.

Tools required for replacing Core Plugs

  • Safety glasses
  • Soft-headed hammer
  • Flathead punch
  • Pliers
  • A new set of core plugs
  • Sealant
  • Socket set

Types of Core Plugs

Note: Core plugs come in various sizes. It is important to know the exact measurement of your engine’s core plugs before you buy new ones.

Shape type

In terms of their shape, core plugs are primarily of two types:

  • A cup type.
  • A domed-disc type.

Both are similar in functionality; the only difference is how they are inserted in the core holes of the engine.

Material type

Core plugs are also available in different materials. The core plugs made out of steel are pocket friendly, but they might not last that long. So, if you are looking for something that is more durable, you should get core plugs made out of brass.

Dismantling the Engine

Accessing core plugs can be difficult with the engine still intact in the car, and you might also end up damaging other components while reaching for the plugs. So you need to take the engine block out of the car by dismantling the engine. It might appear as a daunting task since the engine itself is quite heavy to lift. You might require some additional help to get the engine block out.

Following are the steps for taking out the engine block:

  • You will first need to drain out the coolant from the engine.
  • Before dismantling the engine, make sure you disconnect your car’s battery and wiring to avoid any accidents.
  • Now carefully disconnect any hoses, lines, or other components like the radiator and thermostat from the engine.
  • Unbolt the engine block using the appropriate tools. If any bolt is broken, remove the broken bolt
  • Once loosened, get extra help to remove the engine block out of the car.

Replacing the Core Plugs

Following are the steps for replacing the core plugs from an engine block, once it is out of the car.

Step 1: Place the engine block on a flat surface.

Step 2: Remove the older core plugs by inserting a screwdriver at the sides and gently hitting it with the hammer. Be careful not to damage the core hole.

Step 3: Once loosened, the edge of the plug would project out, take a pair of pliers and pull the core plug out. Make sure you pull it out straight, or else it might get jammed in the engine’s core hole.

Step 4: Use sandpaper to even out the edges of the core hole and remove any residual remains of the older sealant or coolant.

Step 5: Apply a fresh coat of sealant on the new core plugs and insert them one by one in the core holes.

Step 6: Use a flat head punch of the appropriate size to push a disc-type core plug in with the dome facing outside. If you are using a cup-type core plug, then use a socket of the right size to push the plug while tapping it with a soft hammer.

Note: Don’t push the core plug more than a few centimeters in, or it might fall inside the engine block and be difficult to extract.

Step 7: Let it sit for a while for the sealant to sit in.

Step 8: Get help to lift the block again and place it where you first removed it from.

Step 9: Bolt back the nuts which you removed.

Step 10: Carefully reconnect all the components that were detached.

Step 11: Wire back the wiring. Since you are already rewiring the system, this can also serve as an opportunity for you to replace your car’s car lights and significantly improve the car’s illumination.

Note: Before you reconnect the battery make sure that you have a perfect car battery. A faulty battery would not allow the engine to operate properly.

Step 12: Reconnect the battery. Ensure that the battery leads and connections are in correct place.

Refilling the coolant

Once everything is reconnected, it is now time to refill the coolant in the cooling system through the radiator or the overflow tank. Ensure that the draining valve is closed; otherwise, the coolant might get wasted.

Before turning on the engine top it up with an engine oil to ensure that it functions smoothly. Now turn on the engine and take your car for a drive to ensure everything is functioning fine.

Core plugs prevent the coolant from leaking outside the engine. Knowing how to replace core plugs comes in handy in case of a coolant leak from the core holes due to corroded core plugs.

The whole process of replacing the core plugs might come across as very time-consuming and complex, but learning how to replace core plugs and investing in durable core plugs can benefit you for a long time. Performing the replacement, yourself can save you a lot of money.


Leave a Comment

Your email address will not be published. Required fields are marked *