80w90 Gear Oil.... which has a distinctive smell---doesn't smell like regular oil. I can't really explain the smell---but you'll know it once u smell it..if it's black---then it's best to change it...if it's clear golden---it's good----sometimes you'll get a dark cream color...looks like cappachino-----this sometimes can be a sign that u're oil seals are going--and water is getting into the oil chamber. Usually most pumps take like 150 ml of oil.