Replacing Core Plugs
Core plugs are put in place to prevent damage from coolant freezing inside your engine block. If you think that coolant is leaking inside your engine block, one culprit could be a leaky rusted core plug. For this task, you will need a new core plug, Dremel tool, flathead screwdriver, hammer, needle nose pliers and a socket.
It will depend on the make and model of your car if replacement of the core plugs will be easy. Some cars have the core plugs situated at the bottom of the engine block, and it will be easy to access just by lifting. Some require you to lift the engine block, the transmission, or both, to access the core plugs. The rule of thumb here is that you must have enough space to swing a mallet or hammer, because you will need these to put the new plug in place.
• The first step is to determine which core plug is leaking. Using a hydraulic jack and a couple of jack stands, lift the front of the car. Make sure that the car is securely elevated because you will be going under the vehicle to check. Add water to the system and then quickly make your way underneath your car. Watch out for dripping. Core plugs are small dish-like plugs located at the bottom edge of the engine - they are in an area close to the cylinder heads as well.
• Once you've made sure which plug is compromised, remove the coolant from the system by draining it entirely. This step helps clean the entire system as well as makes installation of the new plug easier and less messy.
• Take the flathead screw driver and, placing the tip against the rusted plug, tap the screw driver with the hammer and start turning the core plug until it comes loose. Lightly tap on the screwdriver until the plug is seated inside the block sideways. You can now use the needle nose pliers to pull it out.
• Line up the new plug in the hole left by the old core plug. Hammer it gently into place.
• Do the same for the rest of the core plugs. Even if only one plug is rusted, it might be a good idea to replace the whole set, due to the time and labour required.
• Once you have replaced the core plugs properly, replenish the cooling system with water and start the engine. Let the motor warm up for five to ten minutes before checking for leaks and other problems. If there are no signs of leaks, drain the water and refill the system with an the proper proportion of water and coolant (or anti-core). But if there is still a leak, you might have to retrace your steps to make sure you've fixed the leak properly. The leak might actually be located elsewhere in the cooling system.
In some cases, you can use rubber plugs as a temporary or emergency repair solution. These can easily be tightened with a wrench. Using rubber plugs might work as long as metal ones, but it might be a good stopgap measure; at least so you can bring the car to the garage for repairs.