Now days 99% of the cars use 5W30
I'm going to have to disagree with that, Denny. many late model vehicles (say, last 10 years) are calling for 5W20 as the preferred grade. Ford has specified it since at least '98 on some models, all vehicles by 2000. Honda, Toyota, and Chrysler also specify 5W20. In the case of the Chryslers with the Multi-Displacement setup, use of anything but 5W20 will disable the system, as it is very sensative to the oil viscosity. GM seems to be the only real holdout on 5W20, calling for 5W30 in pretty much all of their gas engines.
Something that's coming down the line (next 2 years) will be 0W20 full synthetic (yes, ZERO). Toyota is already suggesting it for use in their passenger car engines, and I've heard from a reliable source that it will be the required oil in Toyotas by '12.
On topic, I use straight 30 Valvoline Super HPO in the '55, still redily available at most parts stores, plus the local TSC that about a mile from my house carries it. I did try 10W30 (which I use in my '85 S10), but the 235 seemed to run "happier", for lack of a better term, on the 30.
