Some where in one of the topics in the BITOG forums I remember seeing something about 0W oils in place of 5/10w Oils. And not for the life of me I can't find it again. Anyway, I thought I remembered reading something along the lines of people now preferring to stick with a 5w over 0w oils. This is by no means a quote of anyone, but I remember something along the lines of 0w oils either having a higher NOACK percentage, or a higher break down rate which leads to high deposit and sludge build up on engines due to the higher viscosity spread? I apologize for my ignorance here, but my memory is not as good as it used to be. Is this really the case? Should I think about moving back over to the 5w20 and 10w30 oils that my vehicles originally came spec'd for in place of the 0w oil's I've been using? I've been using them with the thoughts of quicker start up lubrication and the possibility of improved efficiency. My 3.8l Mivec Mitsu engine calls for 5w20 "For Maximum Fuel Economy" with a note of 10w30 being acceptable for temperatures greater than 0 deg. This engine gets used the way an engine is meant to be. Although I wouldn't say that the engine is abused (however many might disagree) but I do run it through its RPM range, and It does see its share of WOT from time to time. I figure I make up for it with the 50miles of easy HWY cruising I do with it each work day lol Anyway, the car has 65k on the ODO, and only is driven in the warmer season. Stored for the winters. Because I do drive it hard, and the fact that the oil recommendation seems a little fishy (almost as if Mitsu would prefer a 10w30 oil but have to push the econ on us. I've owned several Mitsu's throughout the years and they always wanted a 10w30 oil. It has seen a strict diet of Amsoil 0w30 oil. Originally TSO, and then replaced my SSO once it was released. More recently it has been juiced with LM Mos2. Through the oil fill hole, the valve train looks extremely clean from what I can see. I've also bore scoped the cylinders out of boredom and the pistons are extremely clean with no carbon build up. Last year I removed the lower oil pan to install an oil temp sending unit in the pan. While I was in there, I noticed there was a light film coating on the lower end. Everything was clean as can be except for that light coating. I was able to wipe that away with paper towel. I've read on the forums that this is not unheard of with Amsoil. For whatever reason it may leave some staining. If this is true, I don't see anything that could be a cause for concern. I will be replacing the timing belt in the near future, and at the same time will remove the valve covers to adjust valve lash. At that point I should be able to get a better idea of what the valve train looks like. My other main concern vehicle is an '11 5.7l Hemi truck. I changed out the factory fill with Amsoil ASM 0w20 (factory rec is 5w20) and have been using it up until my last oil change. Currently it has PU 5w20, but when it's done I will go back to Amsoil. I have no idea what the inside of this engine looks like with 24k on it, but I'm sure it looks totally fine. So, all being said; is there any truth to the avoiding the 0w oils? Am I not looking out for the best interests of my prized engines??