Uneven heating and sudden cooling of auto glass - Your experiences

Joined
Dec 10, 2013
Messages
925
Location
Kuala Lumpur ,Malaysia
Just as a thought experiment, or perhaps something like this did indeed happen to any of you.
Say you parked your car at a semi covered area, and the lower half of your windshield is exposed to the extreme summer sun, and the upper half in the shade. Or the whole windshield is exposed to summer heat, then you decided to go for a car wash. In any of these cases, did anyone experience cracking of the glass due to thermal stress ?
 
It doesn't quite fit your parameters, but I once bought a car that had a 4"-6" horizontal crack in the upper third of the windshield, starting at the edge of the driver's side. I made a day-long trip in December, and noticed the next day that the crack had gone completely across the windshield. I was in southern Kansas and northern Oklahoma after dark during the trip, in cold conditions with some snow or sleet. I'm fairly sure that's when it happened, although I didn't see or hear it with the defrost blasting, music, and road/engine noise.
 
Having the windshield half in the sun and half in the shade should not affect the glass temperature. Glass, with few exceptions, is transparent to solar energy. Solar energy must be absorbed by a material to produce heat, so glass would not heat up on it's own but the materials in the car would heat up. They would heat the air in the car, which in turn would heat the glass. I have known a few people that have used hot water instead of an ice scraper when the windshield was frosted over and cracked the windshield.
 
I've only seen one instance where it was clear that temperature was the cause. I knew someone in Wyoming who had a heated garage, and when he pulled his truck outside into the sub-zero temperatures, it cracked in several places.

I've owned a couple of cars where a crack originated at a far edge, underneath the windshield trim, and running the defroster made the crack run across the windshield as I drove. It's fun watching money fly out the window.
 
Yes, I've cracked a car windshield from heat and sudden cooling. My Camaro was parked in the sun. I sprayed the windshield with a hose in the washing process and cracked it top to bottom. No differential in the temperature across the windshield though. It was all very warm.
 
Having the windshield half in the sun and half in the shade should not affect the glass temperature. Glass, with few exceptions, is transparent to solar energy. Solar energy must be absorbed by a material to produce heat, so glass would not heat up on it's own but the materials in the car would heat up. They would heat the air in the car, which in turn would heat the glass. I have known a few people that have used hot water instead of an ice scraper when the windshield was frosted over and cracked the windshield.
Well here is the thing. I was curious so I my car is parked with approx. 3/4 the windshield covered and the other 1/4 in the sun. after 20 minutes the ambient is 70f, the top of the glass is 107f and the lower exposed to sun is 117F . So I guess a differential temperature is possible .

Oh I forgot to mention that I have 2% tint on that same window. So I am sure with no tinting the sun exposed temperatures would be greater. And yes I thought of your next thought.... the interior at those same exterior temperature measurement's were 83f and 95F.
 
Years ago I was told by a Washington, D.C. guy that windshields "crack all the time" when people start their cars and turn the AC on.

I don't know how much truth was in his statement. Next time I'm in a hot town I'll ask at a glass shop.
 
I had an OE Toyota/Asahi windshield crack on me. It was a hot day, my car was parked near the river and I had to use my windshield washer to clean things up. The next day, there was a crack running on the lower half of the glass.

What I do now is if the windshield is too hot to put a hand on, no water contact or sudden chilling. I try to start the HVAC with a reflective sun shield up before removing it.
 
One of the hottest days I can remember, and we were on our way back from a day of boating. We stopped to get an ice cream, and parked in the sun. Came back to a truck with an interior so hot it was hard to touch, and a huge crack through the upper 1/3 of the windshield. No idea how or why.
 
If that was a problem, then factory windshield heaters (and even rear defrosters) would shatter the glass.

It only cracks in extreme differences, such as pouring boiling water on a frozen windshield, where the temperature difference is 200 degrees

Car washes don't use boiling water, nor do they use ice. Temperature difference is much smaller
 
existing cracks will expand. i ran my windshield heater to melt the ice on a sub zero day and the crack expanded.
 
Back
Top