hi all:) have a 1998 toyota corolla, 71,000 miles. last oil changei did, used oldish texaco 10w30 dino oil i bought 10 years ago,walmart clearence, sm, 79cents a quart...so bought all they had left.lots. burned ovr 2 quarts of oil and it was black looking at dipstick,1,700 miles and 2 months in :x so! discovered and read about rislone engine treatment,which my local walmart and autozone carry. bought a quart...it says too add a quart of rislonetoo 4-6quart sump capacity...i topped off 2 quarts of mobil 10w30 semi synthetic, and added 1 quart rislone..leveled it off.. was i supposed too replace a quart of oil with rislone? or add rislone too 4 quart fill capacity? i read use 2 quarts for a dirty engine,...is that added too 4 quarts, or do i replace 2 quarts of oil for 2 quarts of rislone?