I did some more digging just to see how oil temperature follows coolant temperature. I found these charts posted by members of a
BMW forum. As I anticipated, oil temperature lags coolant temperature pretty drastically as Oil Pan's pressure information suggested. Of course, I'm not sure where this oil temperature sensor is located. I would guess that it is inside the oil pump. So, the oil wouldn't have time to be heated by the engine block much. Once it has been pumped through the engine it will obviously pick up heat. However, without a temperature sensor in the return flow of the oil we have no way of really knowing. But, we really want to be pulling warm oil to begin with. Its not just the friction of the engine that is reduced with lower viscosity oil, its also the work that the oil pump has to do as well. Pumping thicker oil and thus having higher oil pressure requires more power from the engine.
These charts show two different trips. The first one is a city drive he did, the second one shows a trip to his work with some highway driving. From the charts you can see that coolant temperature starts around 30C / 86F, so this is obviously a summer drive. Coolant temp hits ~100C after only about 3 minutes of driving. How long does it take the oil to warm up to that temperature? Nearly 20 minutes! By that time, my car would have already been sitting in my work parking lot for about 5 mintues.
