Somehow 20 degrees Fahrenheit doesn't sound to me like a temperature that would necessitate grill blocking, and it doesn't sound like cold winter weather for Wisconsin, but Daox has the coolant temp data to support this step, so what do I know.
I do remember my Dad, and others of his era, recommending putting a big rectangle of corrugated cardboard, between the radiators and chrome bumpers of their 1950-60s American sedans and station wagons, when the coldest part of winter arrived (10 to -20 F.) in northern Illinois, where we lived at the time. Then, later, my wife and I would have to tape over most of the grill slots on our air-cooled 1977 VW bus (the grills were on the upper rear sides of the vehicle) for the engine to kick out enough warm air to defrost the windshield in the worst part of winter. And surely others have seen the radiator covers on long haul semi-trucks--they even have zippers on them now for adjusting how much of the grill they cover or leave open! Daox, what about zippers?
There is something I don't understand, Daox: In post #2 of this thread the LARGE lower grill area is open, but, in all of the other posts, your pictures show the large lower grill area blocked, too. Why would you need to block that little slot if the entire large grill is blocked? Did you write about how you blocked the large grill in an earlier thread?
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