OK today I went for a run and kept an eye on temp gauge.
Just to refresh, I have blocked both upper and lower grille on the car now so there is none/very little airflow coming through to the rad.
Today was a hot one, it was 31°C (88°F), it very rarely goes above 33/34°C (93°F) so I could pretty much judge today if I could run year round with these blocks on.
My temp gauge went to 98°C (208F) one way, 96°C (204F) on the way back. I didn't employ any hypermiling techniques as I wanted constant load on the engine for accurate temps. The fan comes on at 102°C (215F) on my car so I would say averaging 97°C on a sweltering hot day like today is pretty much a success.
I hit 45MPG / 37.5MPG (UK/US) without using any hypermiling, this is a new record, but not until next weekend and I travel to the city 50miles away will I get a clear picture of just how effective it is where this route is where I do my calculations on every time.
But for me, this is what it's all about
I hope it's still this fun when there is no improvements to be made and you just take your great milage for granted.