Advances in engine oil technology and increased combustion efficiency has resulted in the longer oil intervals in vehicles. Current oil change interval practice only takes into account the mileage a vehicle has driven and does not consider other vehicle operations that affect oil life like extended idle. Routine oil sampling is one way to ensure optimal oil intervals, but the price continuous analysis can be prohibitive. It is possible to use on board diagnostic (OBD) data to correlate oil degradation to engine usage in order to develop an algorithm that is applicable to many vehicles. While much research has been conducted for light duty vehicles, little has been completed for heavy duty vehicles, in particular vehicles that idle a majority of their time. This study uses multiple heavy duty vehicles that are monitored by monthly routine oil analysis and logging of on board diagnostic data to determine the effects extended idle has on the wear rate of oil. The vehicles were used in their normal operation; this resulted in an average idle run time of 60% of run time and no less than 50% in a single vehicle. At each sample the quality of the oil and the operation of the engines were assessed. The results of the oil analysis showed very little degradation of oil. As expected, a negative correlation was seen in viscosity and total base number (TBN) but not abnormal when compared to base oil. Significant degradation was not seen even after using the vehicle passed the manufacturer recommended oil intervals. Analysis of engine operation showed that the temperature of the oil was optimal for 85% of idle operation. In addition, oil pressures at idle were sufficiently higher than the minimum pressure recommended by the manufacturer, but was less than half of the average in use oil pressure. The combination of low pressure and optimal temperature has resulted in little oil degradation. The results from the study have shown that extended idling in the study vehicles can be treated similar to long trip interval service for oil degradation. Additionally, extended idling did not result in abnormal engine wear or excessive contamination.