That is completely ignorant, sorry!
You should not mix chainsaw oil into the crankcase of a car!
If you really need some sort of increased viscosity to quiet an older
noisy engine I recommend Powerpunch.
The oil turning black is completely normal and OK, this is expected as
carbon blowby gases accumulate in the oil.
Still I guess you are just trying to destory the engine? So good luck to you.
PS mixing various viscosity oils doesn't work, they will seperate like
different sized marbles when they sit in the crankcase.