how much higher can the temperature be inside a vehicle
The seats in both vehicles were cloth. RESULTS Within 20 minutes, readings in both cars exceeded 125 F and reached a maximum stabilized temperature in 40 minutes (Figure). The temperature rise in the first 10-minute interval was more severe for the dark-colored enclosed sedan than for the light-colored minivan. The maximum stabilized temperature was also higher for the dark enclosed sedan (140 F compared to 138 F), which was a temperature rise of over 45 F in less than 1 hour.
The best way to raise an engine's temperature to optimal levels is to drive it almost immediately after startup; according to a study by the Ontario Ministry of Transportation, a car driven for 12 minutes in 14-degree-Fahrenheit weather will achieve the same temperature as one that idles for 30 minutes.