My dad had a Subaru SVX with the six cylinder engine. He used Mobile one synthetic. And a mobile one synthetic filter. He changed his oil at 8000 miles. He showed me how the oil looked like new.We laughed about it,I poured it into an old M1 gallon jug and you couldn't tell it was used. His car was like this the whole time he owned it. Why? Did it stay so clean? You had to look hard to see it on the dipstick. I later used the oil after throwing some other new oil I got free, In with it.