Core plugs are found on the sides of the engine block. They fill the holes used by equipment to hold the core in alignment when the molten steel is cast to form the block. Later the holes are used to remove the sand used in the casting process. The holes go into the cooling system, so when the plugs corrode through, coolant leaks out. The plugs are often referred to as "freeze plugs" because if there is not enough antifreeze in the coolant, the water can freeze. Water expands when it freezes and will push the plugs out. Sometimes that will prevent the block itself from cracking, but that is not their purpose.
To replace the plugs, the old one must be pounded in with a hammer and punch on the edge to cause it to spin so you can grab it with a pliers. The new plug is pounded in with an installing tool that puts the pressure on the outer lip. The plugs are soft metal so they will conform to the size of the hole.
The hardest part of replacing the plugs is gaining access. This is almost impossible without having the car on a hoist. On some engines there are also plugs on the back, hidden by the transmission.
As for the battery drain, the easiest way to find it is to remove fuses until the drain stops. Interior lights is a good place to start. Suspect a glove box light or trunk light that isn't turning off. Computers can also fail to turn off.
Sunday, March 28th, 2010 AT 2:23 AM