Improving an IC Engine’s thermal efficiency by heat preservation by providing: heat insulation layers to the cylinder, piston crown, combustion chamber and cylinder-head including internal gaps/cavities with or without vacuum; reduced carbonisation of fuel and oil; reduced the thermal shock by exhaust gas recirculation - EGR with control/intake valves, heating and storage tank; improved thermal shock resistance of insulation with flexible/porous thread/fibre and cloth materials bound together by binding with paste, stitching, weaving, braiding or pressed/clamped together; improved distortion resistance using sapphire or tungsten steel; an elongated piston cap or cone; segmented or annular sheet cylinder/liner construction; direct or indirect cooling of fuel injectors with fuel recirculation or spark plugs with high pressure gas jets in pits or slits.