A blended dye for use in a coolant. In one embodiment of the invention, the blended dye includes a first water miscible dye adapted to fluoresce when illuminated with a light. The first dye preferably has a wavelength of about 340 nm to about 420 nm. The blended dye also includes a second water miscible dye adapted to fluoresce when illuminated with a light having a wavelength of about 400 nm to about 460 nm. The second dye has a different composition from the first dye.