This morning I choose to drive my wife's 2010 to work as we're in a stiff, cold air blast, +25 mph, 43 F, headwind for first six miles. I had expected the exhaust coolant loop to quickly warm-up the coolant and it did, right up to 70C and then it plateaued. This sort of makes sense as 70C is all that is needed for hybrid operation. Normally the engine heads to 82C when the coolant thermostat opens and in hot weather up to 92-95C (fan turns on at 95C.) In the cold, dense air, headwind, MPG into work did not break 50 MPG. However, I suspect bumper radiator inlet blocks would have brought it back up. Early tests several years ago with a full, cardboard block showed a measurable reduction in vehicle drag. Bob Wilson
See that all the time here in the "cold white north". I installed A/C system pipe insulation a week ago (it's more flexible than the standard ethafoam pipe insulation) in the lower grill, fully blocking it. Pearl S now warms up to the 80s C after about 20 min. Still have to do the upper grill, perhaps this week. It's just below freezing here and has been for a few weeks now. We even have snow. Want some?
