Originally Posted by PaleMelanesian
What about a black hood, with copper pipe running back and forth, also painted black (maybe on the underside?). Feed the loop of piping through the cooling system. It'll preheat the coolant.
Andrew, I like the idea! I'm sitting here looking at a flexible heating pad with loops embedded in it and wonder if something similar could be made to carry coolant:
A roll up black mat with insulation on the underside to protect the car (perhaps also it could cover the windshield / roof to keep the interior cool?), liquid tube loops with quick disconnects to the engine's coolant system, and a flexible solar panel attached to drive a pump. A quick search found a 12v pump rated at 600 LPH that only uses 18 watts.
Not much weight involved except for the coolant?
Justin, any comments as you are familiar with solar water heating? I have no idea of what quantity of coolant in the loops would need to be, or the velocity of the coolant to give it time to pick up the heat.