Abstract: Målet med projektet är att ta fram ny kunskap om de energieffektiviseringspotentialer som finns med att använda motorvärmare i en nyare fordonsflotta. Projektet syftar till att minska kallstartseffekter, vilket ger minskad energianvändning och lägre avgasemissioner. Projektet kommer också att undersöka vilket uppvärmningsalternativ som kan ge störst bränslereduktion vid kallstart; värmning av kylvattnet eller av smörjoljan. Projektet förväntas bland annat ge rekommendationer om hur motorvärmare bör användas under olika förhållanden. Abstract: To drive a certain distance, including an engine start, always leads to higher fuel use and emissions compared to driving the same distance without an engine shutdown. By using a block heater it is possible to substantially reduce the cold-start effects. However, these effects must be balanced with the increased energy use of block heaters. In this project, a simulation model is used to find the optimal use of block heaters for various drive systems and requirement levels taking into account different parking times, air temperatures and mileage. An analysis is also performed on the resulting cold start effects on a regional and national level due to optimal use of block heaters on the basis of travel habit, number of starts etc. The project will lead to thorough and detailed basic data that can be used for educational purposes and to develop computational routines leading to an optimal charging time that is vehicle specific.