0W30 is NOT the same as 30. Straight 30 is just that. The viscosity remains at 30 in it's operating range. "0W" is the Winter designation and means the oil's viscosity will drop to 0 in it's cold operating range and raise to 30 as it heats up.
Check your owners manual. Most of the mfgs. of newer engines suggest using synthetic and multigrade oil over single grade oils for certain temperatures. Check your OM to be sure.