[orange4boy]

I seem to be making some mileage headway with the pre warming. 6.3 L/100K cold 5.3 L/100K warm. So far this is what I have done:

Grille blocks. Upper is two pieces of closed cell 3/4" pipe insulation. they fit right in woth some judicious slots cut for the little grille tabs. Lower is an internal coroplast piece screwed to the honeycomb. there is a 6" section left open for a bit of cooling. I'd like to make this adjustable.

Engine blanket. This is 3 pieces of sound deadening material with foil on the engine side and a layer of rubber between. This is great at keeping the engine warm during stops.

Gap sealing around headlights and hood. This keeps the warm air from escaping and it really helps.

Front belly pan in coroplast. Keeps drafts out.

Passive inline coolant heater. AKA lower radiator hose heater. I have this installed on my upper hose though because the Prius has it's thermostat where the lower hose enters the engine. Gives me about +20˚C coolant temperature.

To do:

Block heater

Tank/circulation engine heater for the transaxle. Since I already have the engine preheat sort of worked out I will try the circulation heater in the tranny because it hasn't been tried AFAIK. (plus it's easier to set up) As Bob and others have documented, the cold tranny eats a lot of energy. Since I already have the synthetic WS ATF in there, warming is the next step.

Oil pan heater for both the transaxle and the engine.

Better get going...