1. how good is shell gas? i've always used exxon/mobil in my car.
2. can it damage your car's engine or anything if you switch between brands of gas (i.e. if i switch on and off between exxon gas and shell gas, will it do anything to my car)? (stupid, i know, but i'm poor so i don't want to do anything that would damage my car and thus cause me to be in a dilemma financially to hvae it fixed.)