No. CNG does not have any known harmful effects on your vehicle. The absence of any lead content in CNG helps avoid lead fouling of plugs, thus enhancing plug life. Upon entering the engine in the form of a gas, CNG does not disturb the presence of lubricating oil in the engine, and reduces chances of wear and tear. Further more, it does not contaminate or dilute crankcase oil, giving a new span of life to the engine.