Reducing friction in crankshaft bearings during cold engine operation by heating the oil supply to the main gallery has been investigated through experimental investigations and computational modelling. The experimental work was undertaken on a 2.4l DI diesel engine set up with an external heat source to supply hot oil to the gallery. The aim was to raise the film temperature in the main bearings early in the warm up, producing a reduction in oil viscosity and through this, a reduction in friction losses. The effectiveness of this approach depends on the management of heat losses from the oil. Heat transfer along the oil pathway to the bearings, and within the bearings to the journals and shells, reduces the benefit of the upstream heating. Results show that step increases in temperature produced at the gallery inlet can be maintained along the pathway to the bearing inlets, but heat transfer from the oil film in the bearings outwards through the bearing shells and inwards to the bearing journal greatly reduces the benefit. Simulations show that insulating the film from both the bearing shells and journal is necessary to realize the potential of pre-heating the oil.