Tracer Products' Dye-Lite fluorescent dye, No. TP-3100, pinpoints engine oil, hydraulic fluid, lubrication fluid, compressor oil and gearbox oil leaks. Add a small amount of the dye to the system and allow it to circulate for several minutes. Then scan the system with a high-intensity UV or blue light lamp and the dye glows bright yellow. The dye can remain safely in the system until the oil is changed.