My friend's Acura RL has a 1-ft long crack starting from the right edge of the front windshield, about halfway up the windshield. It's roughly horizontal, with some up and down deviations, but no "spider web" or "sunburst" cracks at all! He noticed it after the car was parked in a parking lot. What could have caused that??? He thinks it was vandalism.
He can rule out vandalism, which leaves a big smash (the voice of experience!)
The most common cause is the effect of temperature changes when there is a rock pit in the glass. I moved to cold country about 5 years ago and learned cold nights cause most of the cracks here. Our Toyota dealer made the determination whether our windshield crack was a defect covered under warranty or damage to report to our insurance by running a ballpoint pen along the crack. It hung up in a pit, indicating it was damage that had grown into a crack... no warranty. It ran from the bottom edge near the driver to the left edge and appeared when we washed the car after it had been sitting in the sun.
As TeGGeR often points out, it is important to be sure it was not rust of the weld around the windshield that did it, because the next windshield will suffer the same fate if the rust isn't repaired.
Ah. I've had the displeasure of watching a crack form (but at least my newly cracked windshield was clean!) and it spread several inches per second once it got started.
On a related subject we took a cab in Mexico (Puerto Vallarta? I forget) recently and I noticed there were several nearly complete circular cracks, about an inch in diameter, in the windshield. As I pondered what caused those, I realized there was a more normal crack that ended inside each of the circular ones. Then the light came on - the circular ones were made purposely to stop the spread of the normal cracks... like stop-drilling them. It still looked weird.
Our 04 RX330 had a stress fracture crack. The dealer determined it wasn't due to a rock chip, vandalism or anything like that and replaced it under warranty.
So, if the crack is really smooth from the side of the windshield to the end of the crack, there is a chance it could be a stress fracture.
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