Month and a half update:
It is still working
As the temps drop I can leave it closed for the the whole trip if it is a short on (less then 8 miles) On the freeway at hypermiler speeds I need one grate open (half of lower grill). At the speed limit 65 or 70 MPH I need both both open above 54 F One is fine till the ambient temp drops below 35. then I can close and open as needed.
I need to see if I am getting any leakage as it still takes a while to warm up (4-5 miles) when the temps are under 40 F.