Running efficiency of LHR diesel has been confirmed by mean of well-known types of heat-insulating (HICs) or thermal barrier (TBCs) coatings. These materials are considered as a semitransparent media SHICs (STBCs) in the form of an ensemble of diffraction objects, forming own thermoradiative fields under the scattering theory laws. This problem is relevant for a diesel with combustion chamber (CC) in which intensive IR radiation reaches ~50% of total thermal flux. The authors indicate that predetermined selection of optical and thermoradiative parameters in the same spectrum for coatings (due to specific structural composition and porosity) can change their temperature fields inside its subsurface zone and hence in the CC gas volume. Previous author's research of optical parameters for ceramic semitransparent materials allowed offering SHIC (STBC) samples for rig testings. Optically simulated absorption and scattering indices for SHICs fix their thermoradiative fields which determine the formation of optimal temperature profile inside ceramic coatings at the type conditions of diesel CC operation. A number of the latest rig testings of diesel engines with coated piston by PSZ-ceramics were studied from the point of influence on the radiant heat exchange by semitransparent coatings deposited on the CC internal surfaces. Analysis and reasons of reducing the specific fuel consumption at high speeds using SHICs (STBCs) were carried out. In view of the known literature data on rig testings of LHR diesel and also experimentally measured optical parameters of semitransparent and opaque coatings it became possible for the first time to calculate correctly its temperature fields. Subsurface heating of semitransparent ceramic coats specifies the possibility of thermoregulation for the piston surface with SHICs (by varying its structure) in contrast to the use of opaque HICs. Such PSZ-ceramics were recommended for application and improvement of operating conditions of diesel CC piston protected by means of coats with selected optical and thermal physical characteristics. The usage of the suggested methodology in contemporary industry enables to intensify significantly R&D for LHR diesel and to ensure advanced management of its combustion-exhaust system temperatures, the required regime of thermoregulation for heat-insulated CC wall surfaces and generation reduction of the most toxic NOx.