A little bit background on the car. The car is a 2004 1.5 Vios. Prior to being passed to me, my dad used it as an everyday car and I had no idea how he maintained it. The car was given to me as my daily driver and I had changed the intake and removed the catalytic converter. When I eventually took over its maintenance, I peeked through the oil cap and noticed some varnishing in it. So in an effort to remove the varnishing and hopefully remove the sludge I did the following steps:
1. Oil Change at short interval - the way that I did this was that I change my oil using mineral type at 500km-1000km. Every oil change I used 1 liter of oil to use for flushing.
2. Then I used Mag 1 All fleet and added Seafoam (both through intake and mixed with oil) and ran for around 4000km

Confident that I had somehow overcome the problem, I used Liqui Moly with BT 223 for around 7000km. Liqui Moly is probably the best oil Iv'e used, the engine was running silently and smoothly. Then I noticed an oil leak on the upperpart of the engine. The mechanic told me that its probably time to replace my engine cover gasket (not sure if correct). I scheduled the replacement of the gasket with my oil change. During the oil change, the mechanic and I were surprised that the Liqui Moly still retained most of its color, it was dark brown but not black probably due to the oil filter (props to doc for this). However, when the top of the engine was removed lo and behold! sludge everywhere! the mechanic immediately recommended that an oil pan cleaning and oil strainer (not sure, but the part that suck oil from the bottom) needs to be cleaned. When he removed the oil pan, it contained so much asphalt....err sludge. So now, I'm selling the car haha just kidding! a change engine would be a good option later on. But its hard not to think about the other parts of the engine that still had the gunk when I'm driving it. Moral of the story: Want to change engine? don't maintain it .

Engine cover half cleaned (Picture was taken via phone so its not too clear)


Oil pan with asphalt


Bottom of the engine


Sludge