Gr8 stuff! What is all this crap about waxy build up?!? Waxy build up comes from not changing your oil and filter when you should. Any moron knows that. I have been using PZ since 1995 in my following vehicles... 1986 FORD F150 5.0 V8, 1993 F250 5.8 V8 HD, 2000 Dodge Durango 4.7V8, 2006 Kia Optima 2.4 I4. just to name a few. When I got the durango it had a fair amount of sludge (2 years ago) Owner serviced it frequently, (4.7 is notorius for sludge because they don't breathe good) and when i got it i replaced the PCV valve, and started running PZ. Not only after 3 oil changes at 1500 mile intervals did it clean the engine out, it also stopped the loud chattering valve train. Think about that one I cant argue with other's personal experiences, but I can argue that this stuff will not sludge up your engine if you change your (censored) oil!