My car gets hot in summer and I was looking up online ways to keep it cool. Most of the advice was what you’d expect (keep the windows rolled down half an inch when you are parked, use a reflective windshield visor) but some people claim dumping a bottle of water over the top of the car will keep the inside cool when you park it.
I assume since hot air rises, as the hot air reaches the roof it’ll heat the roof and eventually the heat will be absorbed by the water via conduction.
Is any of that true (I don’t know how the hot air inside the car would manage to heat the metal on top of the roof outside the car)? I guess I could try it. Would it matter what the humidity in the environment would be?
The water won’t last but a few minutes and there’s far too much heat for a bottle of water to absorb to the point of making a difference.
One personal-size bottle of water? I imagine that would lower the temperature .01º for .01 second – if that.
Now, a tanker car full of water would cool things down a bit. But note that it would cool down a hot car. Pouring water on top of the car as a preventive measure is folly – as soon as it has evaporated (which won’t be long), the car will heat up as if nary a drop had touched it.
If you really want to keep it from getting hot, park it in shade, or in Fairbanks.
One personal-sized bottle of water isn’t going to do the trick, but I’ve found when I wash my car with a water hose it cools the car off. A word of warning, though: cold water on a hot windshield can extend any cracks or chips you have, so cool your car down carefully.
I wouldn’t expect it to be nearly as effective as leaving the windows open, using a sun visor or parking in the shade. Evaporation of water is a very effective cooling mechanism. It would reduce the temperature of the roof significantly, but the inside is insulated, so I wouldn’t expect it to cool the air inside the car a great deal.
Be careful with water. I once attended a soccer match in the summer, when the air temperature was 100 degrees, and I parked my car in an outdoor parking lot. I lowered my windows some, but the car still got incredibly hot inside. As I was leaving the lot to get to the main road I happen to drive through a sprinkler that spayed water directly on my hot windshield and it cracked immediately. Hot glass combined with cold water can be a bad combination.