What's the 2005 mazda 3 oil type?

Your 2005 Mazda3 will have either a 2.0L or 2.3L 4Cylinder engine under the hood. Both engine variants recommend the use of 4.5 quarts of SAE 5W-20 synthetic motor oil, though the use of SAE 5W-30 is okay over the short period. However, if You must do this, it's recommended that You swap it out for the recommended oil at the first opportunity -- else, You risk premature engine wear because of inferior viscosity. When You're reading an oil's weight, the numbers represent viscosity at different temperatures -- the first, at startup, and the second, at operating temperature. Lower numbers are better, so using SAE 5W-20 will keep Your engine running more efficiently with less friction -- which can allow You to keep Your Mazda3 on the road for years to come.