Last weekend I helped my cousin put a 400 into his bronco and we got everything going and running. Sounds great until you turn it off. When you turn it off it has a violent clickin noise that shakes the whole truck. You can tell that it is something in the coolin system. We made sure to purge all teh air out and still did it. It sounded like the thermastat so we replaced that with a new one and it continued to do it. Just wondering if anyone knew wtf is going on??? thanks........I dont know much about fords and wondering if it had to something with that engine or a common thing.