Drain coolant . Take sharp punch or screwdriver and poke hole in freeze plug. Then pop freeze plug out of block. When making hole in freeze plug don't hit hard enough to damage cyl block behind plug as there isn't much area between block and plug. When installing new block heater, make sure electrode does not touch interior of block. The worst thing you can do to a engine mounted block heater (not tube type) is to run engine with heater plugged in. Air bubbles may form on electrode and burn it out sooner than normal.