Abstract: A frost plug adapter assembly having a locking mechanism that provides a positive capture through an existing frost plug aperture. A cylindrical body is engaged within a frost plug aperture and is maintained in place by a bolt, a locking element and a wing nut. The bolt is advantageously positioned through the cylindrical body with a bolt head at the outer end. The wing nut is screwed onto a threaded end of the bolt so that the wings engage channels of arms of the locking element to spread the arms until they contact an inner annulus of the frost plug aperture. The frost plug adapter assembly is also capable of providing access to engine fluid by providing channels through the inner end of the cylindrical body. The frost plug adapter assembly is easy to install and the locking mechanism prevents the assembly from falling out under severe conditions.