I started my Tahoe up in the garage at 46F and drove about 15 miles on a county blacktop to the interstate in 20F ambient temperatures. The graph ends about 3 minutes after I got on the interstate. The Tahoe has louvers over the radiator that stay closed until the engine coolant temperature is > 180°F. The closed radiator louvers help the engine coolant warm up faster and prevents the charge air cooler radiator from being cooled. The engine coolant and charge air coolant are two completely separate systems. Warmer charge air also help the engine warm faster. There is a thermostat in the charge air coolant loop that maintains the charge air temperature at about 90F. When everything is up to temperature the charge air will stay around 90°F even when the ambient temps are well below zero. When ambient temperatures are at or above 75°F the charge air cooler system doesn't have enough capacity to keep the charge air at 90°F and the charge air temp will creep up. The highest charge air temperature I've seen is around 140°F when the ambient temp was +95°F. Keep in mind that the compressed air temperature post turbo is highly correlated to intake air temperature. If the intake air is 0°F the high boost post turbo temperature will be around 250°F. If the intake air is 100°F the high boost post turbo temperature will be around 350°F.
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