In this paper, the effect of the thermal barrier coated (TBC) on top of the piston used in CI engine was investigated when diesel and mahua biodiesel (MB 100) were used as fuel. Three pistons were selected for TBC with a thickness of 0.05 mm as a bond coat and 0.25 mm as a topcoat. The first piston was coated with 7% YSZ (LHR 1), second piston was coated with 2%Nd + YSZ (LHR 2) and third piston was coated with 5%Nd + YSZ (LHR 3) as a topcoat for the three pistons Ni–Cr–Al–Y used as a bond coat in all coatings using plasma spray technique. The exploration of work is performed in a four-stroke, single-cylinder naturally aspirated diesel engine. In this study, standard engine with diesel and mahua biodiesel with three different TBC pistons like low heat rejection (LHR 1, LHR 2 and LHR 3) with mahua biodiesel was compared. The study shows that the brake thermal efficiency of an LHR 3 with mahua biodiesel is 11% higher than that of STD engine. The brake specific fuel consumption of an LHR 3 with mahua biodiesel was reduced by 13% lower than the STD engine. The HC and CO emissions were reduced by 13% and 16% for LHR 3 engine when compared to STD engine, but the NOx emission was marginally increased by 18% for LHR 3 engine. © 2020, The Institution of Engineers (India).