Abstract: A fuel oil treatment unit and associated method for removing undesirable contaminants from a fuel oil, such as diesel oil, being delivered to an associated engine, such as a vehicle diesel engine. The invention includes, inter alia, a unit for treating contaminant-containing fuel oil, comprising means for heating the fuel oil to a temperature sufficient to volatilize at least some of the contaminants and, also, means for filtering the so-heated fuel oil, to remove therefrom at least some of the remaining, unvolatilized contaminants. Optionally, the previously-heated and filtered fuel oil is passed to a temperature control means for maintaining or returning the temperature of the fuel oil to a desired level.