have you tried the oil flushing additive from shell? yung nilalagay muna hinahalo sa lumang oil bago mo i flush para ma clear out yung mga oil smudge. effective ba yun mga guys?
Ingat kayo sa mga 'engine flush', hardened engine deposits could be a part already in maintaining good clearances between engine parts that's why many suddenly experience engine trouble after they use these products.

Personally, I use diesel motor oil every other oil change to keep my petrol engine clean.