Did Mrs.ekpolk know there was a different oil in the toy?
Did Mrs.ekpolk notice ant thing other than mpgs?
As to the first, yes, I spoiled things a tad by telling her what I'd done. She reported driving as usual (i.e. fast...), and that the car exhibited nothing unusual to her perception. Of course, I doubt she'd notice anything short of huge orange flames erupting from under the hood, but that's another issue...