Why is transformer oil unsuitable for use as diesel fuel?

Transformer oil is formulated for insulation and cooling, not for combustion. It can contain additives, degradation byproducts, and potentially hazardous contaminants from service, making it unsafe and often illegal to burn. Used oil may include PCBs in legacy equipment, moisture, metals, and acids. Burning such oil can produce toxic emissions and violate environmental and waste regulations. Even new transformer oil lacks diesel fuel specifications such as cetane rating and controlled volatility. Utilities treat used transformer oil as regulated waste or recycle it through approved oil processing channels.