In this study, the feasibility of increasing the proportion of cashew nut shell liquid (CNSL)-based biofuels in diesel was assessed. Biofuel–diesel blends with different percentages of CNSL were prepared, and their physical properties, including the density, viscosity, and heating value, were determined. B10 (CNSL/diesel = 10:90 v/v) satisfied the diesel specifications without preheating, whereas B20 (20:80 v/v) and B30 (30:70 v/v) met the specifications only after preheating to 60 and 80 °C, respectively. To avoid preheating B20 and B30, an acetone/butanol/ethanol (ABE) mixture (30:60:10 v/v) was added to the fuel blends to improve their flow characteristics. The blends with CNSL/ABE (361)/diesel ratios of 20:10:70 and 30:30:40 (v/v) exhibited properties comparable to those of diesel and remained stable for one month of storage. These fuel blends allow up to 30 vol% CNSL and 30 vol% ABE (361) to be incorporated into diesel and can be used as alternative fuels in diesel engines.