After our discussion last week about oil weight and viscosity I did some research.
Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).

Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.

Engines need oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil. You will hear them referred to as multi-viscosity, all-season and all-weather oils. An example is a 10W-30 which is commonly found in stores.
Most manufacturers of high performance engines including turbos and superchargers recommend 5W30. But as Dennis said 10W30 is fine for our engines.

 

Thanks for the long and informative post [img]/w3timages/icons/tongue.gif[/img]

5w/10w is just your winter rating, which doesn't make any difference here in Fla. 30 is the weight. 5w is usually thought of as the 'winter' and 10w as the 'summer' oil: completely irrelevant to us since temperatures here (hopefully) will never go below 0'F. I just had the engine flush and put in Mobil 1 synthetic 5w30 about 300 miles ago, as Mobil 1 recommends it as the oil for newer cars. 10w though should work completely fine as well.