*Car Manufactures’ Dealers do not recommend to use Additives, saying that they don’t do any good to the car. Is this true ?
Many dealers recommend using an anti-friction Additive. Moreover, they do

*Do Gasoline Additives harm the engine’s Oxygen Sensor and the rest of the Injection system ?
Absolutely not. On the contraty, they help the system and decrease pollution emissions without harming the Sensor of the Catalytic Converter.

*Does Top Oil Premium damages the engine if I use it frequently ?
Not at all. Your engine will remain in excellent conditions.

*One I used Top Oil, and the car bécame slower, cranking and issuing smoke. My mechanic told me not to use it again. Why does it damages the car ?
Top Oil was doing it’s job…cleaning the accumulated filth, and that is why your car cranked. It is recommended that in case you have never before used Top Oil, to use first Top Oil Injector Cleaner while at half-gas tank, and then Top Oil when you fill up again the tank.