Seems like oil is becoming thinner all the time......My new 2004 Mazda3 requires 5-20W oil.....Can't help thinking 10-30W or 10-40W offers more protection and wear saving properties.......Any engineers care to explain this?
Rick

Thinner oil has less viscosity, gives slight boost to EPA mileage ratings.

Go here:

http://www.bobistheoilguy.com

You should not use 5W30 oil in hot climates like Arizona or Florida. I use 10W30 or 10W40 in Florida all year round.