What weight is SAE 30 oil?
Similarly, is SAE 30 oil the same as 10w30?
Nope. SAE 10W30 is an oil that has SAE 10W viscosity(thickness) at low temperatures, and SAE 30 viscosity at high temperatures. SAE 10W30 is an oil that has SAE 10W viscosity(thickness) at low temperatures, and SAE 30 viscosity at high temperatures. The W stands for 'Winter'.
Keeping this in consideration, is SAE 30 motor oil the same as 5w30?
No. SAE 30 is a single viscosity motor oil. Only multi viscosity motor oils only should be used in any car. 5W means that the oil at cold temperatures acts like a 5 weight thinner oil.
The Society of Automotive Engineers (SAE) developed a scale for both engine (motor oil grades) and transmission oils. This number represents the oil's resistance to thinning at high temperatures. For example, 10W-30 oil will thin out at higher temperatures faster than 10W-40 will.