Have an oil question ,but not a simple one! First. Have purchased a new sealed 55 gallon drum of old stock oil.Stencil on barrel says (Arcoflt S3P-20 ) Assume 20w but cant seem to find a way to decode. I also have some straight weight 130w oil and if the oil in question is 20w would like to know ratio to mix in 130 weight oil into the 20w oil to make it 30w oil. Hope someone can help. Should make for good conversation!!