Tracer Products' TP-3900 Dye-Lite Coolant/Auto Body Dye finds leaks in radiators, hoses, water pumps and fittings. Just add 1 oz (30 ml) of the dye to a cooling system and allow it to circulate. Wherever the coolant leaks out, so does the dye, which remains at the site of the leak. When the system is scanned with a UV blue/black light, the dye glows a bright green showing the exact location of the leak. Can also be used for pinpointing wind and water leaks. Simply mix the dye in proper dilution with water and spray suspect leak sites outside the vehicle using a TracerJet spray gun.