Save heat, decrease warm up time.

[oil pan 4]

I was thinking about doubling up the hood insulation but it looks like its working pretty well. Looks like I could benefit from weather stripping and somehow installing side insulation.
If there was no insulation the hood would be lit up brightest of all.
I don't think this will keep the engine warm over night, but it could keep heat longer for a stop to the store or make the passive block heaters more effective.

[Frank Lee]

Exactly.

Combined with a grille block to reduce drafts, a noticeable amount of heat is retained for at least five hours (when I commuted and used the vehicle at lunch, I'd stick my hand under the hood at quitting time and could feel warmth. This was in brutal winter conditions. And the defrost and heat came "online" noticeably faster).

When the block heater started two hours before departure (on a timer) you could see the windshield starting to defrost from the defroster vents, and the hood was all covered in snow/ice but it was all melted away at the hood to fenders and cowl gaps. I never tried to weatherstrip 'em shut.