ABSTRACT Investigations on several B, C and D-segment vehicles were done to evaluate the impact of an engine encapsulation on the cooling down behaviour of the engine. Approximately 7K higher temperatures measured in the powertrain after 12 hours cooling down can be expected of such a concept. Main target of heat storage in the powertrain is to reduce CO2 emissions during engine restart due to elevated oil and coolant starting temperatures. Estimations based on measurements and calculations done on a C-segment diesel car resulted in a CO2 reduction of about 1.5 percent in the NEDC cycle after 9 hours cooling down. Two different encapsulation approaches where tested and compared to each other. Assets and drawbacks of both approaches in terms of heat storage capability, thermal safety and weight balance were investigated.