A number of years ago I was in trade school for auto mechanics. The rumor was going around the shop that if you used Quaqer State motor oil, that it was sure to leave a lot of sludge in the motor, and this should be avoided at all costs. One guy points to an engine running Quaqer State that was torn down and notes the sludge. A short time after that I tore down my own engine down that had been run on Penzoil and the sludge was just as bad. Another guy tears his engine down that was running Havaline and the sludge was just as bad as the other 2. A number a years later I see Quaqer State running an ad that their oil did not leave sludge deposts and they showed an engine to prove it, so the rumor must have eventually gotten back to them. Has anyone ever dismantled an engine that wasn't covered up with sludge on the inside????? If so what type of oil were you using??