Only had my car a couple of months when I started to notice a slight misfire. then my coolant was disappearing. Once my car started overheating, then went back to normal temp, suddenly. after some troubleshooting and my own home diagnostics, I came to the conclusion that I was screwed. Coolant doesn't just disappear the same time your car starts misfiring. I've used block sealer and head gasket sealer a million times with no luck. So, I said a little prayer and tried it one more time. I followed the directions to the 't', and I couldn't believe what I was seeing! as soon as I started my car, the check engine light immediately went out, and I haven't had any more problems in that area, and that was many months ago. I think it was Barrs, the one with the little black pellets. I still can't believe it...