Thanks guys,
Sorry about my impatience, Mech, but I was antsy to get the car back & wanted to have something to tell the mechanic in the morning.
In the end, I bought some 0w30 and had them use that. It says right on the bottle it's an acceptable replacement for the 5w30, which is what's written on the engine's oil fill cap. I'm thinking that we'll be going into summer soon, so that's another reason to stick with the 30 weight for this change. Then, maybe come fall, especially if I find out more to indicate it's ok, try the 0w20 over the winter.
I like MetroMPG's suggestion of getting the used oil tested. I've never done that before, so need to learn how. But I'm seeing testing the 0w30 when I drain it, then running the 0w20 over the winter & then getting that tested. Then compare the results (assuming I can even tell what the heck they mean!! LOL!!!!)
EDIT: Oh, also - it seems getting an oil pressure readout on the thing isn't going to be simple, either... The ScanGauge doesn't seem to have any provision for it, even in the customize-able "X-Gauge" menu. And according to the mechanic, there's a weird type of nut holding the "oil light" sending unit on, so it wouldn't be a simple case of plumbing in a pipe "T". That was another big reason I abandoned the 20 weight oil for this change.... not being able to monitor oil pressure was just "too much"..
