Hi all. 91 Plymouth Acclaim, 2.5L 4 cylinder, 124,000 miles. Had purchased this car about 7 months ago from a friend who had kind of been rough on it (7k mile OCI, lots of idling, etc.). Well, I had changed it from Valvoline to Chevron Supreme pretty soon after getting it, and a SuperTech oversize filter. I do not leak oil, I do not burn oil, and the oil stays at a constant level. But, the oil would get dirty fast, so I got some Neutra, added about 6 ounces, and drove about 625 miles, then changed oil. Added 6 ounces to the new oil, drove about 450 miles, then, since I had a highway trip coming up, added about 16 ounces more to the same oil, remembering what Bob had done for a good cleaning, and did the drive, adding about another 200 miles to this oil. So, I have now about 700 miles on this second oil change, and am ready to change the oil, which is a charcoal grey color right now. Now, to the question. While autorx interests me, I have not the money to play with it just yet. The neutra has pretty much killed my cold lifter noise, and has the car running quieter, stronger, and smoother. Ideally, if the M1 T&SUV would get to where I live, I would go with it, but Rotella is cheaper for now, which is a plus, and it is a 5w40, which I truly think my engine would like, as it is the engine from which the 4.0 HO 6 cylinder Jeep engine was built from, and it likes 5w40 from what I have read. So, have I done enough cleaning to go to the Rotella T Synthetic? Aside from the grade difference, will this be an upgrade from the Chevron Supreme 5w30? What OCI would you all recommend, without doing an Oil analysis? I eagerly await your replies, as I am ready to change my oil again...!!