A method of dynamically determining engine oil change intervals for an internal combustion engine having selectable high and low operating speeds HS and LS, respectively. The method includes the steps of accumulating operating time THS of the internal combustion engine at speed HS, accumulating operating time TLS of the internal combustion engine at speed LS, calculating a high speed factor HSF as a function of the accumulated engine operating time THS, and calculating a low speed factor LSF as a function of the accumulated engine operating time TLS. The method then sums the high speed and slow speed factors HSF and LSF to provide a sum S which is compared with a predetermined constant K1. A signal indicating the engine oil should be changed is provided when the comparison step finds the sum S has reached the predetermined constant K1. In a preferred embodiment, the method also includes the step of detecting when the engine oil of the internal combustion engine has been changed, and the step of resetting the accumulated high and low speed operating times THS and TLS, respectively, when the detecting step detects that the engine oil has been changed.