Having my commuter vehicle chill down to ambient temps in a cold parking lot during work was what prompted me to begin experimenting with grille blocks and engine blankets 20 years ago; I was very disappointed that my hard-earned drivetrain heat was being all blown away during the day when parked. I had noticeably faster warm defroster air available with the block and blanket.
Although a thermos hot coolant storage system would take it all to the next level.