The biggest concern with using B-12 Chemtool Fuel System Cleaner (part #0116) in a diesel engine is a reduction in lubricity inside the fuel pump and the fuel injectors. However, even at the maximum recommended dosage of 1 oz/gal, these components should not generally be adversely affected. If you are able to “top off” with additional fuel, do that in order to further dilute the B-12 Chemtool. Speaking of diesel vehicles, we invite you to also keep an eye out for our newly-formulated line of top-quality diesel additives that began shipping just last year. This family of products includes Diesel Injector Cleaner (part #0518), Diesel Cetane Booster (part #0517), and All-Season Diesel Fuel Treatment (part #0512). Just look for the bright green Berryman labels that tout our new “IDI Deposit Buster” chemistry to know you’re getting the best diesel fuel additives on the market.