Plastic pollution is increasing as the management of plastic waste has become a global challenge. The possibility of turning plastic waste into fuel at low temperatures has been successfully reported in our recent research. However, the low recycling ratio and higher fuel viscosity were the main limitations. The focus of this research was to improve the depolymerization process of low-density polyethylene (LDPE) in diesel by introducing various amounts of co-solvents. The resultant product can be directly used as transportation fuel without further refining. Several co-solvents were examined in the LDPE/diesel blend: di-butyl ether, a-pinene, toluene, and o-xylene under various pressures (1, 5, 10, and 20 bar). The quality of fuel products was evaluated using differential scanning calorimetry (DSC), an Anton Paar MCR302 rheometer, and a bomb calorimetric thermometer. The degradation behavior of LDPE in diesel is affected by the co-solvents, and the highest dissolution occurred with 10 wt% co-solvent in diesel. Among the tested reactor pressures, the most effective pressure was 10 bar resulting in 92.4% LDPE dissolution. The addition of co-solvents improved the quality of the fuel blend in terms of the kinematic and dynamic viscosities compared with the PD/LDPE blend. The higher heating value (HHV) of the resultant fuel blend was higher compared to non-solvent, pure diesel-derived LDPE fuel blends. The values of HHV for PD, PD/LDPE (10% a-pinene and 1 bar), PD/LDPE (10% xylene and 1 bar), and PD/LDPE (10% xylene and 10 bar) were 45.24 MJ/kg, 45.60 MJ/kg, 46.05 MJ/kg, and 46.14 MJ/kg, respectively.