A bottle of Cataclean poured into your cars fuel tank (petrol or diesel) is the best tonic you can give your vehicle. The powerful 3-step fuel and exhaust system cleaner removes the harmful carbon build-up that can clog and coat your catalytic converter. Its great for vehicles that have been sitting around or have emission issues, or need an MOT. Step 1 cleans the fuel system, for greater MPG efficiency, step 2 cleans the catalytic converter, reducing emissions, and step 3 cleanses the upper cylinder valve heads and stems for improved performance. 500ml. For best results, use 3-4 times per year.