Why is 5W-50 at $4/qt while others are generally more than that? As you know i'm trying to find a suitable oil (and cost effective) for my 97k mile old 1981 Ford 302 V8. I think using a 30wt oil is too thin, as it seeps past the rings (my plugs were oil covered). Using 10W-40 seems to work, altho I can sometimes smell engine oil!! None of it seems to disappear tho. I was thinking about using 15W-50 or 20W-50 but it seems too thick for winter use. I primarily drive the 81 T-bird in winter weather (0F-30F). By too expensive, I mean anything above $4.50-$5/qt is too expensive.