Low temperature engine oil pumpability studies were conducted using a motored Cummins NTC-400 heavy duty diesel engine set up in a cold room. Comparative performance data were obtained for new SAE 15W-40 and SAE 10W-30 engine oils based on polymethacrylate, olefin copolymer and hydrogenated styrene-diene VI improvers. In addition, used oils from line-haul fleet tests were also investigated. Pumpability tests were conducted at 1800 rpm over a temperature range from -1°C (30°F) to -21°C (-5°F) to determine oil flow times, time to achieve pressurization, and the suitability of the MRV test method, ASTM D 4684, to predict engine borderline pumping temperature (BPT). The study revealed that selection of VI improver plays a significant role in low temperature pumpability performance. The polymethacrylate oils provided the lowest engine BPT and fastest oil flow. Oil pressure instability at low temperature appeared to be caused by air entrainment, and was significantly affected by the choice of VI improver. The engine BPT was significantly more severe than the BPT predicted by ASTM D 4684.