That depends on the density of the chemical you are calling oil.
It they are the same weight oil as in SAE 30 weight oil there is no difference and they are identical. 30 weight oil is 30 weight oil synthetic or conventional.
It can be. The 5w20 is the weight of the oil which you can buy conventional or synthetic. If it is synthetic it will say so right on the container. If it does not say synthetic it is conventional oil.
look in your owners manual and see what weight oil they recommend and then get that weight oil in the synthetic oil that you like.
If you mean 5w20 synthetic the answer is NO. Pontiac recommends SAE 10w30 weight oil in Synthetic or Conventional. Use exactly that weight.
Not necessarily. The w just means it is a winter oil as in SAE 5w20. It is 5 weight when it is cold and 20 weight when it is at full operating temperature. It can be conventional or synthetic. The can will say Synthetic or Synthetic Blend if it is Synthetic.
5W-30 Synthetic or Synthetic blend.
Yes you can mix different brands but I recommend you do not mix different weights. You can even mix synthetic oil with conventional oil. But as the weight of the oil is critical, do not ever mix one weight of oil with another, no matter if it is synthetic or conventional oil.
Use SAE 5w-30 weight oil.
SAE 10w30 weight synthetic oil.
Gas: 5W30 synthetic, gasoline-rated oil. Diesel: 5W40 synthetic, diesel-rated oil.
Use full synthetic 10w30 weight.
20-50w non synthetic