5W20 or 5W30??? Help!

I know the recommendation is to put 5W20 in the Tribute, but many people I have talked to say WHY? When I visited my Mazda dealer last week for my first oil change at 3K miles...he also suggested the 5W30 and that it is what he used...but everything I have read since I had this done makes me want to change it back quickly! I am thinking about calling Mazda about this! Any suggestions for me?

In general new car manufacturers are tending to recommend lighter (lower viscosity) oils for a couple of reasons. One is that lighter oil is easier for the engine to pump so there are less frictional losses which translate into better fuel economy. Along the same lines, light oil can be pumped quickly after the engine is started to the outer reigons of the engine minimizing the time that parts are moving without an oil film present. The reason it is possible to use lighter oil is that the lubrication properties of oil have improved greatly in the last few years allowing low viscosity oil to take the same punishment that until recently only higher viscosity oils could take.

Thanks for the explanation...it helped me understand what is going on here!

Although I intend on using Mobil 5w-20 dino oil for break-in, thereafter I would like to use 5w-30 Mobil 1. Aren't synthetics inherently lighter than dino oil, even if they're the same viscosity? I understand the reservations of someone running 5w-30 dino oil as opposed to 5w-20, but I would think that 5w-30 synthetic would flow as well as 5w-20 dino, all things being equal such as temperature, age, etc.