5w-20 motor oil

Vic Dura · 2005-06-19T11:13:59+00:00

I just bought a new car last month. My previous car was a 1997 modeland it specified 10w-40 motor oil, as had every car I have owned forthe past 30 years. This new car (a 2005 Ford Focus) specifies 5w-20oil. I've since found out that 5w-20 has been pretty much standard forthe past couple of years.Question: Why the apparent reduction in lubricating requirements? Ican understand that theoretically the 5w requires less power to pumpand therefor *might* result in some mileage improvement; but the hightemp reduction from 40 equivalent to 20 equivalent doesn't make senseto me. What am I missing?