WLF-71 Water Leak Finder
WLF-71 is a liquid dye additive which dissolves in water, making the water fluoresce under UV-A ( ultraviolet) light.
This dye additive is commonly used to help locate leaks in large storage tanks, but can also be used to locate leaks in small water reservoirs, such as radiators.
In practice, it is dissolved in the water in the tank and then suspected areas of leakage, such as riveted or welded seams, are examined on the exterior of the tank using a UV-A light.
Any place where the water has leaked through the tank will show up as a fluorescent wet spot.