Each Auto-Rx Bottle Contains 12 Ounces. If your current oil has life left no need to change to brand new oil.
Exception would be if your engine has sludge issues. Than change oil & filter and install new PCV valve if applicable.
Two bottles of ARX Plus were added to a 2001 Echo's existing oil.
Oil filter after the "clean phase" showed nothing unusual.
After the "rinse phase" one could clearly see the results captured
in the oil filter.
Rinse Phase oil filter after 2500 miles.