Just thought this was interesting. The FSM for my 57 Plymouth lists either SAE5 or 5W20 as the viscosities to use for cold weather operation. Most folks think of 5W20 as a newcomer, but it was recommended by a vehicle mfr over 50 years ago! Kinda takes the idea about 5W20 being introduced for CAFE, and blows it right outta the water...I don't think they had CAFE in 1957!