I have an '04 Silverado with the 4.8 liter V8. I don't see any external leaks but my coolant keeps going low. I have to keep topping off my coolant or my engine will run too hot. Do any of you know what the issue could be? I have heard of cracked cylinder heads if they are from Castech. I can't find a whole lot when searching for Technical Service Bulletins. Thanks.