Coolant Temperature Question

[Atrais]

So I recently installed a PLX OBDII gauge and have noticed something odd with the coolant temps. I'm actually running hotter on the freeway at around 70-72 mph than I am cruising down the backroads at around 60 or the surface streets at 35-45. I'm getting temps from 206 in the morning to 212 in the afternoon (88-90 degree ambient temps). Can anybody else offer any insight? Does this seem normal? Gauge cluster temp needle shows normal (big surprise) but I'd think at freeway speeds my temps should actually be lower vs backroads or surface streets.

I'm due for an oil change so I may flush the coolant and go with a higher concentration of water for the summer. Cooling system is basically new (all was swapped in ~6k ago):

New OEM thermostat
New OEM water pump
CSF Radiator
New Radiator Cap

I did look in the manual and see full open for the OEM thermostat is right at 212 and I've never gone over this, but it seems a bit on the high side and why I'm hitting it at freeway speeds and not lower is odd to me.

 

[Salonika]

You are working the engine harder on the highway (greater load = more heat generated)? I know it seems like the engine would run cooler due to increased air flow, but it's really the thermostat that controls engine temp more so than airflow (as long as airflow is within design specs). Anyway, that's just my guess....

 

[Atrais]

Yea the higher load=more heat makes sense but I should think the increased mass flow across the radiator would be able to compensate (previous experience with other cars backs this up). I mean this thing has the aerodynamics of an brick too so I was hoping someone else might have some numbers.

 

[nckwltn]

2nd that. Run at 4k rpm up a big hill for a couple of miles and mine will get up toward 220.... more work = more heat

 

[Fasteddy]

Metal or plastic tank radiator? Radiators must be maintained if possible, replaced if not. Looking at Temps across a working temp core with a temp gun is diagnostic.