Hi Dexter
I think your stat is poorly, the top temp is about right at 80 but my '88 300SL heats up to temp in about 2 miles.
The simple way to test the actual stat is to take it out and put it in a saucepan of water on the stove and heat it up - you should see it open as it gets hot! although you need to take it out to do it (and you might get some earache from any non-carloving female partners)
You can sometimes tell whether the water is flowing through the stat wrongly by feeling which water hoses are getting warm when you start the car from cold though I'm not sure of the "Water flow" on an "8" (mine's a 6 cylinder and I think the cooling system pipes are laid out differently)
cheers
Jim