Castrol cleared the sludge out of my engine. Got my truck which had some in there and started using Castrol and have used it since I bought it. Works great. Not saying other oil would not do that but Castrol proved it is good so I keep using it. Valvoline is good too and it was the first oil so that is definitely a thing to remember it’s lasted this long so it must be good.I've never used Castrol, strangely. Not that I have a logical reason, my father just told me it would sludge stuff up because it did so in the 70s maybe. He was always a big Valvoline fan, so I inherited that I guess. I've heard rumors of Castrol sludge and varnish here and other places online, but part of me still wants to try this forbidden fruit of oil. I do remember Castrol advertising the absolute most as a kid on TV in the early 2000s with the Nickelodeon slime style sludge commercials.
I still enjoy changing oil.