Loading views...
Last updated on

Prepping for a heatwave (Part 5): Hot car

By The SHTF App Team

The father at the gas station ran inside for four minutes to pay, and came out to a back seat that had gone from warm to dangerous in the time it took to buy a soda. He was lucky: his daughter was old enough to unbuckle and climb out, crying, but fine. The number he learned afterward: on an 80-degree day, a car interior can hit 109 in twenty minutes. “Four minutes,” he told everyone who would listen, “and I would have been a headline.”

A parked car is not just a metal box, it is a solar collector. Glass allows sunlight (shortwave radiation) to enter, but it traps the heat (longwave radiation) inside. The result is a rapid, violent temperature spike that defies ambient conditions. On an 80°F day, the interior of a car can hit 109°F in just 20 minutes.

This greenhouse effect is responsible for the deaths of dozens of children and pets every year and can turn a roadside breakdown into a life-threatening survival situation for adults. By understanding the physics of your vehicle, you can implement fail-safe habits to protect your passengers and mechanical hardening to prevent your car from dying when you need it most. This is Part 5 of the heatwave series.

Disclaimer: The information provided in this article is for general informational and educational purposes only. It is not intended as, and should not be considered, legal or automotive advice.

The Readiness Audit

Is your car a hazard or a hardened asset?

  • Green: You have a back-seat check habit, summer-tested fluids, and water stored inside the cabin.
  • Yellow: You park carefully but have no anti-forget system.
  • Red: You think a cracked window is protection.

If you are Yellow or Red, execute Phase 1 immediately.

Phase 1: The Anti-Trap Protocols (Kids and Pets)

Goal: Build fail-safes against autopilot.

The tragedy of “forgotten baby syndrome” rarely happens because of malice, it happens because of sleep deprivation or a change in routine that causes the brain to go on autopilot. You must create physical barriers to this memory lapse.

  • The look-before-you-lock habit: “cracking the window” does almost nothing to slow the heating process, never rely on it. Use the shoe trick: when you put a child or pet in the back, take off your left shoe and put it in the backseat with them. You will not walk away from the car without your shoe, forcing you to look in the back. You can also use apps with child-reminder alerts, or keep a stuffed animal in the car seat and move it to the front passenger seat as a visual cue.
  • The good Samaritan rule: if you see a child or pet locked in a hot car alone, call 911 immediately, check whether the doors are unlocked, and break the glass if needed, in many jurisdictions, good Samaritan laws protect you from liability when saving a life in imminent danger. Choose the window furthest from the occupant.

The Takeaway: Memory is not a safety system, physical objects are: a shoe in the backseat, a stuffed animal in the front, and a breaking point you have already decided.

Phase 2: Mechanical Hardening (Preventing the Breakdown)

Goal: Keep the car alive in the heat.

Heat destroys cars, it evaporates fluids, expands air, and degrades rubber.

  • The battery killer: we blame winter for killing batteries, but summer does the damage, heat evaporates the internal fluid and corrodes the terminals. If your battery is over 3 years old, have it tested before summer and clean corrosion off the terminals with a wire brush.
  • Tire blowouts: heat causes air to expand, and hot pavement adds friction heat. If a tire is under-inflated, the sidewalls flex more and generate more heat, leading to catastrophic blowouts. Check tire pressure when the tires are cold, and inflate to the manufacturer’s recommended PSI (on the door jamb sticker, not the tire wall).
  • The coolant check: ensure your coolant reservoir is filled to the proper line. Never open a radiator cap when the engine is hot, the pressurized steam will burn you severely.

The Takeaway: Summer kills more batteries than winter and flexes under-inflated tires into blowouts, so the June garage visit is part of heat prep.

Phase 3: Stranded Protocol (Survival in the Oven)

Goal: Survive a breakdown in the sun.

If your engine dies, you lose your AC and your car effectively becomes a solar oven.

  • Stay or go? Generally, stay with the vehicle, it offers shade and is a large target for rescuers. The exception is if you have no water and know help is not coming, then you may need to move to better shade, but do not walk in the midday sun.
  • Ventilation strategy: open all doors and windows to equalize the temperature with the outside air. If possible, orient the car so the windshield is away from the sun, or hang a blanket or sunshade in the windshield to block the solar gain.
  • Hydration logistics: do not store emergency water in the trunk, it gets hotter than the cabin. Keep water jugs on the floorboard of the back seat (the coolest spot) and cover them with a blanket to insulate them.

The Takeaway: The stranded car becomes survivable by ventilation, orientation, and water on the floorboard, not by waiting in a sealed greenhouse.

The Essential Kit Checklist

  • The reminder: a dedicated visual cue object (toy or shoe) for the backseat check.
  • The fluid: a gallon of pre-mixed coolant stored in the trunk.
  • The water: one gallon of drinking water per person, stored inside the cabin floorboard.
  • The shade: a reflective windshield sunshade to lower cabin temps when parked.
  • The tool: a spring-loaded window breaker (Resqme) on your keychain to rescue others.

Scenario Planner (Contingencies)

“The engine temperature gauge is spiking into the red.” The trap: keeping the AC on. The fix: turn on the heat, it sounds insane, but turning off the AC and blasting the heater draws heat away from the engine block and into the cabin. It will be miserable, but it might save the engine long enough to reach a service station. Roll down the windows immediately.

“I’m stranded and the sun is baking the car.” The trap: staying inside with windows up to keep bugs out. The fix: create external shade, rig a tarp or blanket outside the car (caught in the doors) to create an awning, and sit outside in that shade shadow, where the air temperature is lower than the greenhouse temperature inside.

Next Steps

  1. Adopt the shoe trick tonight. Left shoe to the backseat every time something precious rides in back, until it is automatic.
  2. Book the pre-summer car check: battery test, cold-tire PSI, coolant line. Three items, one morning.
  3. Read Part 6: Power outage next, for the grid-down scenario where the heat siege reaches your house and the lifeboat strategy takes over.

Originally adapted from public NHTSA and NWS vehicle-heat guidance (public domain).