Well, Morgs, I've tried the MMO in my new Hyundai, couldn't tell any difference in mileage. Smoother? Doubt it, couldn't tell. It's a new car (05 AccentGT), but I used it in the old Hyundai, 1992 Elantra, 168K on the engine, and received no benefit regarding performance/mileage there either. 5W20, Dino, Syn, 5W30, 10W30, with and without VSOT and/or CD2 SLOB, nothing "feels" different or gives me a verifiable increase in performance or MPG. Yet most everyone here reports all kinds of different effects depending on this or that oil, viscosity, or additive.
Then someone around here maybe Terry, or someone of similar wisdom and education, questioned the wisdom of dumping a clorinated solvent in either crankcase OR fuel tank, and I stopped using it (MMO). I do add a two-ounce shot of Lucas UCL to each 10-12 gallon fillup to butter up the uppers, but truthfully, I'm not "feeling" any difference (maybe I'm just not in touch with my "inner car"
). But intellectually, I suppose I know that the intake valves and upper cylinders getting a little lube on them is for the best in the days of 10% plus ethanol. As wih MMO, the Lucas UCL isn't giving me any extra MPG.
Over time, I expect the little things I do to add up to real benefit, such as my PVC catch-can that perhaps eliminates the need for cleaners (the catch can grabs two teaspoons a week of some kind of brown syrupy gruel that would have wound up in the throttle body), the little shot of VSOT I add when I change oil to reduce friction, and the rotation and proper inflation of my tires. These are real, tangible, beneficial actions that positively affect performance, longevity and mileage.
But sweating out the details of viscosity, dino/syn, solvents in the fuel, or reformulating the oil by dumping in ENTIRE bottles of MMO, VSOT or SLOB? Nah, I'm off that train.
You Morg, you and Terry and MolaKule and RayH, and a few others both professional, and simply well-read and self-studied have counseled moderation in all things additive and I've stuck by that pretty religiously of late, and quite to my car's benefit, methinks.