I run a 4.2 here in MN. I try to run it on the hot side, for more heat in winter but that leads to trouble in the summer months - without the shroud also. I have actually heard my radiator boiling, and need to add water every so often if running it heavily in the hot summer months. I am unsure if the water is actually boiling off, I just know it needs it and I've never had to flush it in fall when I test the coolant freezing temperature. It's always "coolant rich".

The only real advice I can give is for the frost plug. I had one that kept popping out, on my old motor, and I ended up adding another block heater in its place. They install with a V shaped retainer, reminding me of a wall hanger. Add a little slilly-cone and it's all sealed up. Good Luck down there! Too bad you don't really need a block heater...