How to Prepare Your Car for a Heat Wave

To prepare your car for a heat wave, do four things: stock heat-stable emergency supplies that can live in the trunk, keep heat-sensitive items with you instead of baking in the car, protect the vehicle itself with shade, and check coolant, tires, and battery before long drives. The goal is simple. If you break down or get stuck in traffic on a 100-degree day, you want water, shade, signaling, and a way to stay cool, and you want the gear that heat would ruin to still work.

The quick version

• Stock a heat-stable trunk kit: shelf-stable water, shade, high-visibility signaling, an escape tool, first aid.
• Carry the heat-sensitive pieces: power bank, sunscreen, electrolytes, and medications go with you, not in a hot trunk.
• Protect the car: windshield shade, park in shade, check coolant, tire pressure, and battery.
• Plan for people and pets: extra water, and never leave anyone in a parked vehicle.

Why a parked car is the real risk

A parked car heats fast. The cabin can climb 40 degrees or more above the outside air, pushing past 130 to 170 degrees Fahrenheit on a hot day (National Weather Service). Extreme heat is one of the deadliest weather hazards in the United States, linked to thousands of deaths in recent years (CDC). A breakdown or a long roadside wait in that environment is more serious than most drivers plan for, which is why what you carry, and how you store it, matters.

Step 1: Build a two-part heat kit

The single most useful move is to split your car kit in two, because half of what people carry should not bake in a trunk all summer.

Trunk core (heat and freeze tolerant, stays in the vehicle year round):

• Shelf-stable emergency water pouches rated for wide temperature swings
• A reflective windshield shade and an emergency reflective shade tarp or bivy
• A high-visibility vest and an LED roadside marker
• A window breaker and seatbelt cutter tool
• Heat-tolerant first aid basics and a durable case

Grab-and-go pouch (heat-sensitive, keep with you or in cool storage):

• A lithium power bank (heat degrades batteries and, rarely, makes them unsafe)
• Sunscreen, electrolytes, and a cooling towel
• Any medications, per the label and your pharmacist's guidance

For the full breakdown of what survives a hot trunk and what does not, see what is safe to keep in a hot car.

Step 2: Protect the vehicle

• Use a windshield sun shade and park in shade or a garage when you can. It slows how fast the cabin bakes.
• Check your coolant level and condition before the hottest stretch; heat is hard on cooling systems.
• Check tire pressure. Hot pavement plus underinflated tires raises blowout risk on long drives.
• Check the battery. Heat, not just cold, shortens battery life and causes summer failures.

Step 3: Plan for people and pets

Carry more water than you think you need, and electrolytes for long drives or outdoor stops. Never leave children or pets in a parked vehicle, even briefly, and even with the windows cracked. Cracking windows has only a small effect on peak cabin temperature and does not make a parked car safe.

Step 4: Before a long summer drive

• Top off water and confirm your trunk kit is stocked.
• Charge the power bank and keep it in the cabin with you.
• Check coolant, tire pressure, and fuel or charge.
• Tell someone your route and timing, and plan stops in shade during the hottest hours.

FAQ

Sources

• National Weather Service — Heat and Cars
• CDC — Heat and Health
• Ready.gov — Water

Related reading: the El Niño 2026 heat outlook, what is safe to keep in a hot car, and the free Heat-Wave Prep Checklist.