Using the information you have provided and not visually inspecting the roof, the black spots on your roof are more than likely algae. Most shingle manufacturers use copper or zinc coated granules to aid against the growth of algae.
Two-stroke oil (also referred to as two-cycle oil, 2-cycle oil, 2T oil, 2-stroke oil or petroil) is a special type of motor oil intended for use in crankcase compression two-stroke engines.omparing regular lubricating oil with two-stroke oil, the relevant difference is that two-stroke oil must have a much lower ash content. This is required to minimize deposits that tend to form if ash is present in the oil which is burned in the engine's combustion chamber.
For two-cycle handheld engines produced after 2003: Use a 40-to-1 two-cycle oil mix ratio (to aid in the reduction of emissions). This can be made by mixing 3.2 ounces of two-cycle engine oil with 1 gallon of gasoline.se the 40:1 mixture. All of our handheld two-cycle units can operate on a 40:1 two-cycle oil mix ratio. IMPORTANT: All two-cycle engines must run on a mixture of gasoline and two-cycle oil. Operating a two-cycle engine on straight gasoline will damage the engine.