A steady state test procedure has been developed and implemented on an extensively instrumented production diesel engine to estimate the total energy transfer to coolant over a New European Drive Cycle. The test procedure involved segmenting the drive cycle into 26 operating conditions, each with a corresponding weighting factor. The test program consisted of both the steady state tests and a series of transient tests for comparison. The engine instrumentation consisted of a bespoke measurement device to calculate the rate of heat transfer through the combustion chamber walls. The sensors were located vertically down both the inlet and exhaust sides of one cylinder. It was found that the steady state approximation method estimated the total energy transfer to the coolant to within 10% of the transient tests. Differences in the idle speed condition were found to have the largest effect due to 21.7% of the drive cycle occurring at this condition. The steady state approximation method can therefore be used to sufficiently estimate the drive cycle performance for energy transfer if an exact condition is used for a region where the weighting factor is significant, i.e. greater than 15%. Subsequently it could also be used for other parameters, such as fuel consumption.