Abstract: A preheater unit magnetically attachable to the surface of the oil pan of an automobile engine includes an electric heating unit and a magnetic device situated within a rectilinear shell having an open side closed by a non-magnetic heat transfer plate. The heating unit is encased in the plate and surrounds the magnetic device. The magnetic device includes a permanent magnet disposed between two magnetic end portions situated to be operative in the same plane as the outer planar surface of the plate through parallel spaced apart openings in the plate for magnetically attaching the preheater unit to the surface of the oil pan. A temperature control switch within the shell maintains the heat transfer plate within predetermined temperature limits.