No technician would knowingly mix five quarts of clean oil with one quart of dirty oil. However, that is the standard oil change because of oil carryover. Up to 1/2 to 3/4 quart of used oil remains in an engine after a normal oil change. During an Engine Clean oil service with the Oil Tool, the old oil filter is removed and the engine oil is drained. The OIL TOOL is then connected to the oil filter housing with a spin on adapter. Air is injected into the oil galleys and the old oil is flushed from the engine. New oil is no longer mixed with highly contaminated oil -- old oil carryover. Now that the old oil is removed from the engine and to prevent dry starts, a quart of new oil is poured into the OIL TOOL canister and it is air injected into the oil galleys. A new filter is installed and the engine is filled to the proper level. If you are looking for ways to reduce operating costs and enhance engine performance the OIL TOOL should be part of the normal oil change procedure.