An experimental study of plasma sprayed ceramic coatings for internal combustion engine was conducted. Based on experimental results of heat transfer measurements, made both on spark-ignition engine and diesel engine as well as on test stand, it was found that plasma-sprayed zirconia coatings, being partially transparent to thermal radiation, are not effective as heat barriers in diesel engines. The loss of barrier effectiveness is strongly enhanced when semitransparent ceramic coating is covered with carbon deposits. Plasma sprayed zirconia coating insulation effectiveness is reduced with addition of soot on coating combustion surface while the insulating effectiveness is improved with the addition of radiant reflective coating on the surface. The conclusions are based on engine test fuel consumption data and thermal transfer rig experiments.