You may be interested in the ScanGauge II, which allows you to read the exact engine coolant temp, among many other things. The normal operating temp of my 400h is 177-180°F, in any weather. Never saw it go above about 182°, even in 100+° heat. Its usually gets there in about 5 minutes, depending on temp, speed, and heater use. I find that when stopped at a light, the gas engine will shut off during warm-up, even with the coolant temp only in the mid-130° range. I believe the normal temp for operation in electric-only mode is 157°F.
http://www.scangauge.com/products/
You can try the grille-blocking technique to help retain the heat in the engine compartment in the winter, to help improve MPG, reduce warm-up time, and get cabin heat quicker (only useful for hybrids). I have the bumper air slots blocked right now. Just use ordinary dark gray pipe cleaner you can get for $2 a bag, cut in half lengthwise. Cut a piece to length for each slot and stuff it in. There is a lot of info about grille-blocking on the PriusChat website. Here's one thread: http://priuschat.com/forums/gen-ii-prius-modifications/38645-my-attempt-grill-blocking.html