Check all of your hoses for; chafing, holes, splits etc. As well as all of your seals
which you can think of... pumps, tanks
Also, prior to refilling your cooling
system, check all of your other fluids. Both in terms of level(s), and to make sure that they look okay. You don't want to be firing the engine up if say, there's a crossover leak from one system into another. Thereby contaminating another of the power plant's vital systems.