OK the other night coming home from a hunting trip the heat in my Commander faded off to cold air. Found it to indeed be low on coolant. Now I had replaced waterpump (well my 12 yr old did most of the work) earier this year. I know it was full. Upon removal of the rad cap I found a clump of what appears to be a peanut butter like sludge collected at the filler to the rad. So is this the telltale sign of a blown head gasket? I'm hopeful I just did something stupid and mixed 2 dissimilar coolants together.