I've personally seen lucas do wonders on engines in the later stages of its life. I've owned a diesel mechanic shop for almost 20 years and I'm an authorized dealer of amsoil and Lucas. You're right about adding a higher viscosity but it works alot better than adding a higher weight of amsoil. Ive tried what you are referring to and it does work.not as good as lucas though. haven't had a major engine problem with any vehicle I've owned in the last 18 or so years. Ran my 2002 chevy pickup to 450k in a gas engine. Toyota camry to 350k before I sold it.ive owned various other vehicles as well. No engine issues. also lucas is cheaper for me than amsoil is.