[Car Knowledge] Tips for Cooling Down Your Car in Summer

As the editor, I'll share my insights from a Hong Kong driver's perspective on "Tips for Cooling Your Car in Summer." I'll explain why driving in Hong Kong is like taking a "sauna" in the summer. I'll also share instant cooling methods, pre-heat prevention tips , and long-term improvement strategies to ensure you're more comfortable behind the wheel and save fuel.

1️⃣ How can you keep cool in the car during summer in Hong Kong?

Hong Kong has a humid subtropical climate , with high temperatures from May to September:

  • Outdoor temperature : up to 33–36°C
  • Temperature inside the car (exposure to sunlight for 1 hour with windows closed):
    → 40–55°C (with shade)
    → 60–70°C (direct sunlight on black roof)

1.1 Principle of the Greenhouse Effect

  1. Sunlight (including ultraviolet rays, visible light, and infrared rays) enters the vehicle through the glass.
  2. The dashboard, leather seats and rubber parts in the car heat up quickly after absorption.
  3. Objects that absorb heat release the heat energy in the form of infrared rays, but the glass blocks the infrared rays from being released, and the heat is trapped in the car.

1.2 Hong Kong-specific heating factors

  • High humidity : The feeling of stuffiness is stronger and sweat cannot evaporate to reduce temperature.
  • Exposure to the seaside : The salty and humid sea breeze brings humidity and heat, and the perceived temperature is higher.
  • Dense traffic : Air conditioning efficiency decreases in traffic jams, and hot air from exhaust at the rear of the vehicle increases the temperature inside the vehicle.

💡Editor ’s experience <br>In Hong Kong summer, especially in the New Territories or on carpark rooftops, getting out of the car and returning home ten minutes later, opening the door is like turning on a steamer. Even the steering wheel is warm, and the seat feels like it’s been “cooked”.

2️⃣ Instant cooling method (before and after getting on the bus)

2.1 Heat before getting in the car

  • Open the car door to ventilate :

    1. First, open the passenger window and roll it down.
    2. Open the driver's door again and gently open and close it 4-5 times by hand to push the hot air out.
      → The Japan Automobile Association has measured a 5–8°C temperature reduction.

  • Driving with windows down first :

    1. After starting the car, open all four windows.
    2. Drive slowly for 1-2 minutes to use the air flow to remove the heat from the car, then turn on the air conditioner.

2.2 Improved air conditioning efficiency

  • After getting in the car, turn on the air conditioner to external circulation + maximum wind speed to dissipate heat first.
  • When the temperature inside the car drops, switch to internal circulation + moderate wind speed to maintain a cool feeling and save fuel.
  • The air-conditioning vents blow towards the roof, causing the cool air to sink along the top and cool down faster.

2.3 Warmth Isolation Method

  • The Transport Department officially recommends covering the steering wheel and leather seats with cloth or towels when parking for long periods of time to avoid burning your hands when getting in the car.

3️⃣ Preventive Heat Explosion (Preparation Before Parking)

3.1 Parking location

  • Prioritize finding a shaded spot (next to a building, under the shade of a tree). Even if it means walking an extra 3-5 minutes, it’s worth it.
  • Underground or covered parking can cut the temperature rise inside your car in half.

3.2 Thermal insulation equipment

  • Front sun visor : Heat insulation can reduce 10–15°C (silver or reflective film works best).
  • Thermal insulation paper for the entire vehicle : choose UV blocking rate ≥ 99% and total thermal insulation rate (TSER) ≥ 50%.
  • Roof insulation film : reduces the penetration of radiant heat from the top.

3.3 Seat Cooling

  • Use breathable cushions or light-colored chair covers to reduce heat absorption.
  • In summer, choose the ventilation seat function, or connect an external USB fan to blow on the seat surface.

3.4 Slightly open the window

  • Leaving the windows slightly open by 1–2 cm can help hot air escape, but it must be safe (against theft and rain).
  • Some car owners will use rain shields to cover the window gaps.

4️⃣ Long-term improvement strategy (applicable to Hong Kong environment)

4.1 Upgrading the insulation system

  • High-quality insulating glass (double-layer laminated, Low-E glass), although expensive, has obvious cooling and energy-saving effects.

4.2 Installing Solar Ventilators

  • Install the solar fan on the car window or sunroof, and use solar energy to extract some of the hot air when the car is parked.

4.3 Interior material modification

  • Dark leather → Light-colored breathable material can reduce heat absorption and the feeling of being hot.
  • The instrument panel can be padded or covered with sun-protective cloth to reduce reflection and heat absorption.

4.4 Air Conditioning System Maintenance

  • Clean the condenser regularly and check the refrigerant quantity to maintain efficiency.
  • Insufficient refrigerant will slow down the cooling process in summer and consume more fuel.

5️⃣ Editor's heartwarming recommendation for cooling down (Hong Kong practical version)

  1. When parking

    • Cover the full windshield with reflective insulation.
    • The windows are slightly opened 1-2cm and protected by rain shields.
    • Stop in the shade.

  2. Before getting on the bus

    • First, open the passenger window fully and shake the driver's door to exhaust heat.
    • After starting, drive slowly with the windows fully open for 1-2 minutes.

  3. Turn on the air conditioner

    • First use external circulation with high wind speed → switch to internal circulation after the car is cooled down.
    • The air conditioning outlet is facing upwards to cool down faster.

6️⃣ Editor's Tips

The temperature inside cars in Hong Kong is incredibly high in summer. Do not leave children or pets behind . Even if you are out of the car for just 5 minutes, the temperature inside the car can rise by 15°C in just a few minutes, which is extremely dangerous.

If you want to keep your car cool and save fuel, you don’t have to rely solely on turning up the air conditioner. Instead, you should strategically prevent heat buildup before parking, exhaust the heat before getting in, and turn up the air conditioner. This three-step approach is the most effective.

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