The opinion of the majority, gave me the impression, that putting my thermostat back in my 83 gl is the way to go. So with a new radiator, is the 180 or 190, or possibly 200, the one to choose. I have a 180 i just purchased about a month ago. My question is, when reinstalling it, does it matter , which way the thermostat is positioned in the water outlet? I know which side is up and down, i am just not sure if that little hole, which has plug goes on top , or on the bottom. If someone has a picture that would be a great help. Thank you!

this way

Ya, what he said is correct.... I prefer 180's personally... any cooler... ummm no... 195's (or whatever shows up as stock... maybe its 190) are ok too, but I prefer to have my car run at 40% between hot and cold rather than 50-55 or so that way I can see its running kinda warm (like it is now) before it REALLY becomes a problem. I prorbably will need a new radiator within afew months, so thats first on the agenda when the Impreza gets sold.

You'll want that little jiggler valve on the top when you put the thermo back in. It lets a little water bypass the thermo, but more importantly, air in the system, so it needs to be at the top.

...or if your theromstat mounts horizontally, point the jiggler valve towards the rear of the car.