87 535is 145k This is my first fall/winter with this excellent running car which I purchased in the spring.I am currently using Castrol syntec blend 20/50,I live in northeast New Jersey & the past week or so since the temps in the mornings have been hi 30's lo 40's I've noticed slower,longer crank times & 10 seconds for oil light to go out . This morning was a whopping 15 seconds for oil light to go out !! With temp 50 & over engine cranks & starts instantly & oil light is out after 2 to 3 seconds. What oil to use ???