Repete, the grill blocks have almost no effect on coolant temps until ambient air temps rise over 75 deg F. Then things start heating up. If you notice, I left open the lowest valence slot and also a small slot of the lower grill opening. These were critical to keeping things stable for most of the year. In the summer time I have to remove the lower block sometimes.
Also, I swapped out my original thermostat that was opening at around 180 F for one that was supposed to be 195 F, however it runs at 206F. Kinda hot. So now when the grill blocks become a cooling limiting factor I get a little more nervous. I don't want to see coolant temps over 215, ever. It would probably be safe to 230, but I just don't like the idea of all that additional thermal stress on all my engine components.
Well, I decided to throw on some vortex generators and see what happens to my mileage. BAD NEWS! I lost at least 3-4 mpg. Even with slower driving to boot. In retrospect I think I may have chosen too large of VGs, since small children and motorcycles were getting sucked into my wake....
Mileage be damned! Kayaking is so freakin awesome. Off to do some more now.