I have a '72 Electra 225 w/ a 455 big block. Is 10W-40 motor oil better for this car than 10W-30, or is there no big difference? I know the startup viscosity is the same for both types of oil, but I'm concerned about the oil weight being right when the engine gets to full operating temperature.
the feature aaWbb only gives you info re viscosity. The lower aa is, the fluider (less viscosity) it is when temp is cold. the bigger bb is, the more viscous it remains when hot. You will observe that in most cases, most expensive oils are the ones with low aa and high bb. for example, a synthetic oil will give a 10W50 (latest technology even provides 5W50). In your region (I guess quite hot ?), I would recommend a mineral oil (i.e. not synthetic which is like giving caviar to pigs :laugh: ) 15W50 or 20W50.
