Grill Blocking on Classic Model

The simplest way is to slide some cardboard in front of the radiator, behind the central vertical stiffener. New Prius People have more plastic in the way and cannot do that.

 

I've blocked off the grill on my Classic..

What I've actually got is that foil-lined bubble-wrap insulation- I've got a liner on the inside surface of the hood made of this stuff to help keep in the engine heat (and indeed, when its in place, after an hour of driving the outside of the hood does not even feel warm). Additionally, I've got two sheets of this insulation between the hybrid radiator and the main radiator. (This is basically one sheet the size of the radiator, cut in two, with some stick-on velcro discs to hold them together- because of the vertical support and the presence of the horn on the driver's side, it's easier to slip in half a sheet from the passenger side, slide it over, then slip in the other half and attach the velcro together)

I put the insulation between the two rads because I want the engine to get warm faster and to stay that way, but I don't want to risk overheating the hybrid components, especially during warmer weather, hence the small hybrid rad is left exposed in this configuration. This arrangement is good from about 0C to about 10C (you start having to watch the coolant temp as it nears 10C; if it gets too hot, just turn up the temperature on the climate control to bleed off some of the engine heat). As the weather gets colder, the air that makes it around the sheet of insulation does result in engine cooling, so I've got a secondary set of shields made of coroplast (left half and right half, again to get around the vertical support). The driver's side is a simple rectangular sheet that slides in front of the hybrid rad this time, and the passenger side is an L-shaped piece that "rotates" into place, again in front of the hybrid rad- the L shape accomodates the space occupied by the hood latch mechanism.. These secondary shields go in front of the hybrid radiator this time because when it's consistently below 0C, there's absolutely no risk of overheating the hybrid components, no matter how hard or how long you drive the car...

The other aspect of using left+right sides for the shields and insulation is that I can "stage" the installation of these components and also remove portions with ambient temperature, so late fall, as it starts to get cooler and I notice my mileage being affected, I may start with only the passenger side's bubble-foil insulation, then as it gets colder, I'll put in the driver's side as well, and finally add the coroplast front shields as it gets even colder... Similarly, if there's a temporary warm spell, or as we approach spring, I can selectively remove the shields and insulation to compensate..

The front blocking, combined with my spoofing of the coolant temperature sensor reading means that the car is much more fuel efficient in the winter vs. an unmodified factory config.. I can easily get engine shut down and extended stealth periods, even when it's -20C outside..