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.
Tests have been done on Jet Skis and it has been calculated that in two-stroke jet skis (newer jet skis are 4-stroke and burn fuel more efficiently) that in a two hour ride, one ski can dump four gallons of fuel into the water. Two-stroke engines don't last nearly as long as four-stroke engines. 2  The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear a lot faster. 3  Two-stroke oil is expensive, and you need about 4 ounces of it per gallon of gas.