A car's interior temperature can become dangerously hot in the summer, often exceeding 140°F (60°C) within an hour, even on a mild 80°F (27°C) day. The dashboard and steering wheel can reach temperatures high enough to cause burns in minutes. This rapid heating, known as the greenhouse effect, occurs because sunlight passes through the windows, and the resulting heat is trapped inside. The primary danger is heatstroke, especially for children and pets, making it critical to never leave anyone in a parked car, even for a short time with the windows cracked.
The rate of heating is influenced by several factors. The exterior color has a significant impact; a dark-colored car will absorb more solar energy and heat up faster than a light-colored one. The interior materials also play a role, with leather and vinyl surfaces becoming much hotter to the touch than cloth. Parking in direct sunlight versus shade is the most critical variable you can control.
The following data illustrates how quickly temperatures can rise inside a sedan on a sunny day, starting from an outside temperature of 85°F (29°C). The dashboard temperature is particularly critical as it is often the hottest surface.
| Elapsed Time (Minutes) | Interior Air Temperature | Dashboard Temperature |
|---|
| 0 | 85°F (29°C) | 90°F (32°C) |
| 10 | 100°F (38°C) | 130°F (54°C) |
| 20 | 110°F (43°C) | 145°F (63°C) |
| 30 | 115°F (46°C) | 155°F (68°C) |
| 60 | 125°F (52°C) | 170°F (77°C) |
To protect yourself and your car, always try to park in a garage or deep shade. Using a windshield sun shade is one of the most effective and affordable ways to block a significant amount of heat. When you first enter a hot car, immediately open all windows or doors for a minute to let the superheated air escape before turning on the air conditioning. This makes the AC system more efficient and reduces strain on the engine. Be mindful that extreme heat can also damage electronics, cause plastic and vinyl to crack, and degrade adhesives over time.
