Countries from every region in the world have set aggressive fuel economy targets to reduce greenhouse gas emissions. To meet these requirements, automakers are using combinations of technologies throughout the vehicle drivetrain to improve efficiency. One of the most efficient types of gasoline engine technologies is the turbocharged gasoline direct injection (TGDI) engine. The market share of TGDI engines within North America and globally has been steadily increasing since 2008. TGDI engines can operate at higher temperature and under higher loads. As a result, original equipment manufacturers (OEMs) have introduced additional engine tests to regional and OEM engine oil specifications to ensure performance of TGDI engines is maintained. One such engine test, the General Motors turbocharger coking (GMTC) test (originally referred to as the GM Turbo Charger Deposit Test), evaluates the potential of engine oil to protect turbochargers from deposit build-up. In this paper, the authors discuss the impact of typical engine oil components on GMTC performance. Concern about turbocharger deposits is not a new phenomenon, however. In the early 1990s the TEOST 33C bench test was developed to simulate turbocharger coking, and early studies showed a correlation between TEOST 33C results and field issues. A comparison of the TEOST 33C bench test and the GMTC engine test revealed no such correlation between the two tests under the conditions studied. Due to this lack of correlation, a comparison of TEOST 33C response with turbocharger deposits generated during field operation was performed.