Truck has had a small coolant leak for a few months now. Towed the camper last weekend & she was overheating quite bad. So I pulled the rad & cleaned it up & she is running cooler but now it is blowing coolant out the overflow on the overflow tank. I had my rad cap pressure tested & it failed so I put a new one on but it is still doing it. Under normal driving it doesn't seem to do it now but I towed my camper & it is still doing it under load. Upper rad hose it hard on cold start as well. Oil level is not rising & I see no white smoke. When it does it I lose about 4 litres of coolant in a matter of a few miles of driving. Is this enough info to determine if it is head gasket or block? I have read on the other site of some stuff you can dump in that will seal headgasket & craked block leaks. Thermgasket & steel seal. Anyone have any experince with either or any other additive good or bad? I realize that fixing the problem properly is the best solution but I am trying to find a temp fix for now.