Abstract: An improved tool for driving core plugs into the core plug holes of an engine block without having to remove the engine block from the vehicle. The tool comprises an arm support having a fastening means for fixedly fastening the arm support to a plurality of mounting holes normally provided to secure the oil pan to the engine block. A core plug driver having a cylindrically shaped driver head is pivotally connected to the arm support and is longitudinally and laterally adjustable relative to the arm support to compensate for differences in core plug hole locations in various types of engine blocks. A kit including a plurality of differently sized core plug drivers is also provided to permit installation of core plugs having various sizes. The tool provides a mechanical advantage in the installation of the core plugs which permits use in situations involving limited clearance space.