Usually, you cannot assume a trunk is hotter than the passenger cabin. In a published comparison of a parked Ford sedan, the trunk warmed well above outdoor air but stayed notably cooler than the cabin during the day. That is evidence against the blanket claim that trunks are always hotter—not a universal temperature rule for every vehicle.
Is the trunk hotter than the inside of the car?
In the illustrated Ford sedan record described by Dadour and colleagues, cabin air was hotter than trunk air during daylight. The trunk still became much warmer than the outdoor air, and its temperature changed more gradually. By evening, both interior spaces moved toward the outdoor temperature.
The article, “Temperature variations in a parked vehicle,” was published in Forensic Science International on 15 April 2011. Its detailed experiments involved parked cars in Floreat Park, Western Australia, during summers 2005, 2007 and 2008, with measurements taken at several cabin locations and in the trunk alongside outdoor weather measurements. The illustrated Ford sedan record was from summer 2000. In the described hot period, cabin air was 20–30°C above outdoor air and reached a reported maximum of 70°C; the trunk was substantially cooler than the cabin in daylight, though still warmer than outside. Read the study.
This is a specific observation, not a dependable trunk-to-cabin temperature offset. The authors focused chiefly on predicting cabin temperature, so the trunk-versus-cabin evidence is narrower. It does not establish that every trunk is cooler, or predict the temperature in a particular modern car.
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- Dual Fahrenheit and Celsius Scales for Universal Use: features two clear, easy to read scales (0-220°F and -10 to 100°C), allowing you to take precise temperature readings without conversion, suitable for all standard automotive HVAC diagnostics
- Dial Thermometer with Magnifying Lens: the 1 inch dial is covered by a transparent, magnifying lens that enhances readability, providing clear and instant temperature readings even in low-light or tight engine bay conditions
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How hot does a car trunk get?
A trunk can heat well above outdoor air when a vehicle is parked, but the study does not provide one figure that applies across cars and conditions. Trunk temperature depends on the vehicle and its surroundings, and a reading depends on where the sensor is placed and whether it measures air or a heated surface.
For context, the study reported cabin-specific findings that should not be mistaken for trunk measurements: on hot summer days, a black vehicle’s cabin was typically about 5°C hotter than a white vehicle’s; opening the driver’s window by 2.5 cm typically lowered cabin temperature by about 3°C under the study conditions. Neither finding makes a trunk-temperature prediction or establishes that a cracked window makes a vehicle safe.
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Why can parked vehicles heat up so quickly?
Sunlight heats dark surfaces inside a vehicle, such as the dashboard, steering wheel and seats; those surfaces then warm nearby air. The National Weather Service notes that dangerous heat can develop even on mild days and that slightly open windows do not significantly reduce the heating rate. National Weather Service: Children, Pets and Vehicles.
The National Highway Traffic Safety Administration (NHTSA) says an outdoor temperature in the mid-60s°F can lead to a vehicle interior above 110°F, and that interior temperature can rise almost 20°F in the first 10 minutes. These are general vehicle-interior safety figures, not trunk-specific estimates. NHTSA: Child Safety.
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Why a cooler trunk is still not a safe place
A lower temperature than the cabin does not make a trunk safe for a child or animal. NHTSA warns that heat, humidity and poor ventilation make trunk entrapment extremely dangerous. It advises checking the trunk promptly if a child is missing and says children must never be left alone in or around a vehicle. NHTSA also cautions that shade and rolled-down windows do little to change interior temperature. NHTSA: Child Safety and NHTSA: You Can Help Prevent Hot Car Deaths.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to compare trunk and cabin temperatures
If you are measuring temperatures out of curiosity, compare readings taken at the same time and under the same conditions. A digital thermometer or data logger can help; the study used thermistor probes and temperature loggers. For an air-temperature comparison, position sensors consistently and keep them out of direct sun.
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- Record the vehicle, sensor location and time of each reading.
- Note whether the car is in direct sun or shade, along with window or ventilation settings.
- Record outdoor temperature and sun exposure; compare cabin and trunk readings taken simultaneously.
These measurements can describe one vehicle in one set of conditions, not establish a safety threshold. Do not use a thermometer reading to decide whether a vehicle is safe for a person or pet.
Quick Recap
Best Value
- 2 Piece Car Temperature Gauge: this kit includes two standard grade bi-scale thermometers, each with a holder and clip; Ideal for simultaneous or comparative readings across multiple air vents in a vehicle or different systems
- Dual Fahrenheit and Celsius Scales for Universal Use: features two clear, easy to read scales (0-220°F and -10 to 100°C), allowing you to take precise temperature readings without conversion, suitable for all standard automotive HVAC diagnostics
- Dial Thermometer with Magnifying Lens: the 1 inch dial is covered by a transparent, magnifying lens that enhances readability, providing clear and instant temperature readings even in low-light or tight engine bay conditions
- 5 Inch Stainless Steel Probe for Accurate Readings: the long 304 stainless steel probe can reach deep into air ducts and vents, ensuring you measure the core airflow temperature accurately and safely, away from external heat sources
- Portable with Protective Clip Holder: each thermometer comes with a secure pocket clip and a protective holder; The shock-resistant design and lightweight build make it easy to carry, store, and access during on-site inspections or mobile repairs
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
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