For older diesel engines (pre2000) using 2T oil helps. It actually aids in lubrication lalo na pag low sulfur na yung diesel fuel (say V-Diesel by Shell). Same with Biodiesel (from SeaOil for example). I use around 500 ml in a full tank (60liter). Several test were done with these additives and compared to Cetane increasing additive (which do better for engine performance) 2T oil is the most accessible and the cheapest for the increase in performance. For so called injector cleaners sometimes I use the Cyclo product. Parang walang effect. Regular maintenance still the best way to go.

Dunno about CRDi and newer engines. Baka wala na effect.