I have checked my coolant temp under many conditions.
I use a thermocouple probe installed right by the standard temp sending unit and get accurate readings on a digital Fluke DVM.
At temps around freezing, you are lucky to get over 150F w/o radiator cover. With radiator cover closed you are right on the money, Boatcarpenter, about 170-175F at idle.
The t-stat will start to open at about 180 and be fully open at 195F.
It will rarily open at idle, even in the summer.
Highway driving (level road): About 180, the t-stat opens a little.
Highway driving (down hill): Temp may drop to 140 if the hill is long enough, say 5 miles on the interstate.
Highway driving (uphill): With a gross weight of about 24.000 lb and a 7% incline, the temp has topped 200F. Drops a little when shifting down to 3rd gear. Ambient about 75F.
Because of the wild fluctuations, I used the radiator cover in the summer too until last year when I custom made the current plywood radiator cover, which I leave on at all times. It helps a lot in keeping a more constant temp. Now I have the radiator winter cover on and fully closed at idle. Night time temps about 20F.
If your coolant temp hits 220F, then you have a problem. Check coolant. Check gauge. Check T-stat.
Remember that the coolant will lose its efficiency after two year or so and should be changed. If it's not clear, it need to be flushed out and replaced for sure.
Bjorn