Use of B-12 Chemtool Fuel Treatment (part #0116) in diesel engines can contribute to the same problems that running gasoline in diesels can. These include reduced power, noisier operation, decreased drivability, damage to fuel pump and valve train, erratic sensor readings, and mechanical damage to the engine itself. Most of these issues would stem from 1) the ability of gasoline and especially of B-12 to resist auto-ignition (which is the very principle in diesels that initiates the power stroke) and 2) the reduced lubricity of gasoline and B-12 (which can eventually damage the fuel pump and valve train). If B-12 is accidentally added to a quality diesel fuel at the maximum concentration of 1 oz/gal, these problems are fairly unlikely. However, the use of B-12 can still contribute to decreased runability and drivability in diesel engines. Instead, please use one of our fuel additives formulated especially for use in diesel engines: All-Season Diesel Fuel Treatment (part #0512), Diesel Cetane Booster (part #0517), and Diesel Injector Cleaner (part #0518).