OK. My fiancee decided she would have a nose around my car. Which I don't mind at all. However she must have undone caps. Now when I was driving to work I heard a pop. Didn't think much of it. Opened the bonnet and the oil filer cap is missing. With oil sprayed everywhere. I wanted to clean the engine anyway. But my question is do I clean the engine with the car running? Or do I have it switched off?