At automotive refinishing supply houses they sell viscosimeters which could be used in testing.
Samples of gear oil,in baby food jars can be placed in the refrigerator and freezer,and also heated in an electric double-boiler.
With a good cooking thermometer you can test the pour-point viscosity of the oil at different temps and get a feel for what heating will do.
One thing we know,is that whatever equilibrium temperature we achieve in the winter, will be nothing compared to a summer day at Furnace Creek,Death Valley,California,where gear oil would be plenty happy.
At one point,VW as going to use the Schacht',eutechtic (sp?) salt thermal storage system for warm cold-starts.It's a very sound engineering concept.
