Why did you capitalize "heavy"
No, oil smokes when it is burnt heavy duty or not.
When the oil get hot, it becomes thinner and the oil pressure drops. This is probably because your oil pump is worn. Using straight single-weight oil, instead of multigrade may help. The are also additives that may help, although they rarely help for long.
Wrong oil weight
The oil is wrong weight - oil plug is out - will not drain
The weight of 1 cube of heavy oil can vary depending on its density, but typically, a cubic foot of heavy oil weighs around 53 to 55 pounds.
I have always found that 20w50, the heavy weight oil, works best in older vehicles.
use the lightest weight oil possible that lets you keep oil pressure.
standard to heavy duty 30 weight.
You have low oil pressure. It can be a partially clogged oil filter, or it can be the oil pressure sending unit is defective. It can also be the oil pump is failing. Change the oil and use a quality filter such as Purolator, Wix, or Bosch. Make sure you are using the correct weight oil that Subaru recommends and nothing else. If that does not solve the problem then replace the oil pressure sending unit. It the problem persists seek professional help and have the oil pressure checked with a gauge.
SAE 30 weight in the engine and 30 weight non detergent oil in the pump.
I would say you have low oil pressure. Change the oil and filter. Use 5w20 oil or 5w30 whichever your owner's manual lists, and install a quality filter such as Motorcraft, Purolator, or Wix. Do not use any other weight oil. If the oil pressure is still low stop driving the vehicle and seek professional help.