..

I've used seafoam every 2-3 oil changes(as a crank case solvent, before draining the old oil) for most of Suzy's career as my daily pony...she still likes about 3/4 of a quart every 1000, whether it be lead foot'n around back & forth to work, all hiway to & from Moab, or grunting up & down trails...

She likes 1.5 qt every 2000...so...basically 2 qt between changes.