My finding was, I need to have an adjustable grill block. I watch the water temp on the ScanGauge. I used chunks of foam pipe insulation. Usually several pieces duct taped together to fill the open gaps in the grill.
For really cold days, say below 10ºF, a tiny opening about 3x6 inches is enough. Maybe don't even need that in very cold weather.
Now with temps between 60-70, I need about three openings that size. I know I'll need more when it gets warmer in summer.
In my case the smaller grill opening increases under-hood temps which supplies my warm air intake.
