I got a vs ecotec, ive replaced the radiator, top and bottom hoses, thermostat, radiator cap, and water pump. But the overflow tank keeps losing water and isnt visibly leaking. I topped the oil up and went for a drive and checked it again and it was about a half inch below full. Drove the car the next day and checked it when I got home and it was about a half inch above full. And the overflow tank was nearly empty. It also stalled twice while i was driving. But started back up. I had the plenum chamber fully cleaned, and it has oil in it now??, and what looks like metal shavings?? Any ideas what could be the problem??