SAE 5w30 oil is an oil designed for cold and warm temperatures. It is basically a 5 weight oil when it is cold and becomes a 30 weight oil when it reaches full operating temperatures.
5w20 is a little thinner at operating temps than 5w30
The main difference is cold flow ability. The 5w30 will flow better when cover over the 10w30. Once operating temperature is achieved, they are virtually the same.
The weight of the oil and flow rate. The 5w30 will flow easier when cold than the 20w40. It is 5 weight oil when cold whereas the other is 20 weight when cold. When the oil reaches full operating temperature the 5w30 is 30 weight oil and the 20w40 is 40 weight.
He 5w40 oil is a thicker oil at full operate temperatures than the 5W-30 oil.
The main difference is that 5w20 is thinner at operating temperatures than 5w30. They both have similar cold flow ability.
5w30
-30
30 is a little more viscous (thicker) at operating temperature than 20.
The w refers to oil weight, or viscosity, the higher the number the thicker the oil. 10W 30 and 5W30 are formulated to change viscosity depending on temperature, with lower number being thinner for winter driving. Generally, 5W30 is better for winter and 10W30 better for summer, or 10 W 40 even better for summer. Check the car manual to be sure for specific type of vehicle.
5w30 oil is thinner in cold weather at 5 weight, and is 30 weight at full operating temperatures. 10w40 is heavier in cold weather at 10 weight and heavier at full operating temperatures at 40 weight.
Both have similar cold flow abilities but the 5w20 is thinner than 5w30 at operating temperatures. Typically 5w20 will be thinner across the whole temperature range than 5w30, but the cold flow ability is close to the same, thus the 5w rating on both.
jaguar recommends 5w30