By Jim Kerr

I received a sunshade in the mail the other day for a trial test. You know the type. It sits inside the windshield of your vehicle, covered in highly reflective foil to reflect the sun’s heat away from inside the passenger compartment. It was from Auto Expressions, formerly known as the Axius line of products. Amazingly enough, sunshades have really only been marketed commercially since the mid 1980’s and that now familiar folding cardboard sunshade with the huge sunglasses picture on them was one of the first popular models.

According to information provided by Auto Expressions, a folding accordion style sunshade keeps dashboard surfaces an average of 23.8 C cooler and blocks 99% of the sun’s direct ultraviolet rays. I was curious about these statements, so I did a little digging and research on my own.

Even though it is well recognized that interior vehicle temperatures get extremely hot when a vehicle sits in direct sunlight, there is not much public information on how hot it gets. The auto manufacturers do their own testing, but this is more for vehicle durability standards than public information. General Motors and Chevrolet in combination with Safe Kids Worldwide are again raising awareness of the dangers through the Never Leave Your Child Alone information campaign but little is given in facts or figures. They do point out that temperatures even as mild as 15.5C (60F) can create dangerous temperatures inside a closed vehicle in minutes.

One of the better studies available was done by Jan Null, Adjunct Professor, Department of Geosciences, San Francisco State University. In her report, “Study of Excessive Temperatures in Enclosed Vehicles”, August 2003, she measured interior vehicle temperatures of different coloured vehicles while they were sitting in the sun. While several tests were done, here is a typical example of her results. On a 25C (77F) cloudless day, the vehicle interior temperature reached 35.6C (96F) in ten minutes, 41.1C (106F) within twenty minutes and 43.3C (110F) in half an hour. Letting the vehicle sit for a full sixty minutes, the temperature continued to climb to 50C (122F). Letting it sit longer had no appreciable increase in interior temperature.

Both dark blue and light grey vehicles were used. We all know dark vehicles heat up more. Right? Wrong! While exterior surface temperatures may differ, Null found only minor differences in interior temperatures. Even opening the side windows 1.5 inches made little difference in the end results.

Medical specialists recognise that heatstroke can occur when a person’s body temperature reaches 40.6C (105F); death at 41.7C (107F). Higher humidity levels also decrease the body’s ability to disperse heat, as does smaller surface areas. Children are more at risk than adults because of their smaller size. The U.S. Centre for Disease Control made a report to Congress stating that cars parked in direct sunlight can reach internal temperatures of up to 55C (131F) – 77.7C (172F) when the outside temperatures are only 26.7C (80F) to 37.8C (100F). You can see that leaving a person in a car while it is parked in the sun could be deadly within only a few minutes.

Sunshades are not designed to protect vehicle occupants, but do they protect vehicles? I tested five vehicles parked in the sun on a 25C (77F) cloudless day. The tests were done between 12 noon and 2:00 PM with the sun directly overhead. The vehicles were a black crew cab midsize pickup, a grey mid size SUV, a navy blue full size pickup, a red coupe and a yellow compact sedan. The yellow car was in the shade and measured 26C (79F). The navy pickup had a sunshade in the windshield and was facing south. It measured 38C (100F). All the other vehicles were facing north and had interior temperatures between 36C (97F) and 38C (100F).

I moved the yellow car into the sun and temperatures immediately climbed. Within 15 minutes they measured 32C (90F). They were 41C (106F) after sitting for a full hour. I then cooled the vehicle and placed a sunshade in the windshield. After sitting for 30 minutes, the temperature had risen to 33C (91F) and slowly climbed to about 37C (99F) within an hour.

Even though I tested the sunshade in the windshield of the vehicles facing north, it had little effect. The back windows were tinted and provided some heat protection. I suspect a sunshade in the rear windows would have had more effect on these vehicles.

In the navy pickup, I removed the sunshade. Temperatures immediately started to climb. From 38C (100F) with a sunshade, it rose to 46C (115F) within 15 minutes and 49C (120F) in 30 minutes. The sunshade was obviously working.

While my testing is not very scientific, it did show me that there was little difference in temperatures based on vehicle colour, and that sunshades do help keep temperatures lower. High interior heat dries out lubricants on moving parts, warps plastics and cracks dashboards. While I could not test Auto Expressions claim of blocking 99% of UV rays, it seems obvious that a solid reflective sunshade blocks sunlight, protecting the interior from fading.

My conclusions: park in the shade when ever possible, and use a sunshade to protect your vehicle’s interior when you can’t. Parking facing North may help but more research needs to be done. And remember, don’t leave any person or animal in a parked car even for a couple minutes on a sunny day. Interior temperatures quickly rise to deadly levels.

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