I would hope that their formula has improved because in the 1970s one of my fellow car enthusiasts used Quaker State in a 1972 Chevelle and faithfully changed the oil and filter at 2500 mile intervals. (He purchased the car new) One day we pulled the valve covers and were horrified to find a white-ish kind of material...... almost like a sand in the cylinder heads. After cleaning the heads we both swore that we would never again use Quaker State. Once my friend switched to a different brand of oil, the problem did not return. I am sure that improvements have been made but as the saying goes, Once bitten, twice shy.
