Abstract: Oil changing apparatus including an oil storage tank and a gasoline powered air compressor, both mounted on the bed of a trailer. An oil hose communicates with the storage tank, and connects into a motor being serviced. The drain plugs of motorized equipment serviced by the oil changing apparatus are provided with quick coupling connectors. The oil hose has a cooperating connector at its distal end, which connects to the modified drain plug. The drain plug connector includes a normally closed valve, to retain oil in the sump when the oil hose is not attached thereto. A first air hose enables the air compressor to draw air from the storage tank in the oil drain mode. Oil is removed from the serviced motor by suction. In the purge mode, accumulated old oil is rapidly purged from the tank. A second air hose conducts pressurized air from the compressor to the storage tank, which forces oil from the storage tank when emptying the same. An accessory enables purging an oil filter cartridge with the novel apparatus.