Well in my experience, little 1.6 liter Civic engines run like crap on 20W-50.
I had a '94 Civic in hot and humid southeast Asia and the engine and gearshift vibrated like mad, because 20W-50 is too damn thick, even in 93ºF weather. Poor little engine struggled to idle, fighting such a thick viscosity.
I disregarded the recommendation for 20W-50 and ran Mobil 1 5W-30, using 10,000 km intervals.
My cousin still has that car, and the engine runs great 9 years later.
20W-50 in a Civic is just plain wrong!
[ November 26, 2003, 05:40 PM: Message edited by: quadrun1 ]