Quaker State 1

In 1990 My friends father built a 327 for his chevy truck and he swore by quaker state. He changed the oil every 3,000 miles and when the truck had 15000 miles on it he found a set of corvette heads that he wanted to use. When he tore down the engine it had about a 1/4" of sludge in the valve covers. needless to say neither he or I have used quaker state since.