I bought a new 1988 VW Golf GTI. I was driving 108 miles per day round trip. I switched to Amsoil synthetic oil at about 15,000 miles. As of August 2003 the GTI had 235,000 miles on it and was still getting 33/35 mpg. My oldest sister is still driving the car and it's never had any engine work done on it. She continues to have the Amsoil oil and filter changed every 5,000 miles.