Im running a 200ox66 on my champ.It has quicksilver oil in it now and has always had it in it.Can I add a blended oil directly in the oil tank or is it imperative to drain tank first?Why do it at all?well,regular oil is 24.00 a gal. and I can buy the blend for12.00. Dont want to ruin a good engine,but,if it wont hurt anything why not?I need some experienced opinions before I do something stupid. Thanks,R.B.