Thermal (?) Cracking


Senior Member
Southwestern Pa.
I just searched and didn't find anything on this subject. Is that because it's never happened to anyone else, (except me) or is it just such common knowledge (except to me) that it's never needed to be mentioned?

Been out salting all night. I wanted to use a different truck for the rest of my daily routine, so I started it (93 Chevy) up and let it warm up. There was ice frozen to the windshield under the snow that was there. Between one thing and another, the truck warmed up for about 20 minutes, defrosters going on high. As I opened the driver's door I *watched* a crack make its way across the bottom third of the windshield. Looked further and saw that it extends almost the entire way across the windshield angling up at about 45 degrees on the passenger side. Outside air temp was as low as 14 degrees.

The only thing I can think of is that the temperature difference between inside and outside caused this. Anybody else had this happen? Was I stupid not to know it would?

(Kinda put a damper on my good "been out doing snowplow stuff" mood too...) :(


Senior Member
Sierra's, Ca
That has happened to me in one of my cars. Did the same thing...let it run with defroster on high for alot longer than I intended. As the car warmed up a small amount of snow slid off the roof and "goodbye" windshield.

Western Michigan
Yep, same thing happened to me this winter. I had a huge amount of snow on the truck, (12" +), and let it run while I went inside. Split all the way across.

Winterworks Veteran
I think that era of chevys/GMC's are very hard on windshields for some strange reason. I have replaced a couple. The windsheild shop told me those windshields are their best seller. Not sure why though.

plowjockey Sponsor
Dayton, Ohio USA
Maybe the best thing would be to let the truck warm up initially with just the heater going and then turn the defroster on low. That way the whole windshield would get a chance to pre-warm and then the defrost heat would not put so much stress in the one area.
The problem with the windshields of that year may be wihtin the specific curvature and thickness, or the proximity to the defroster vents to the glass itself.
Just my $.02 worth of speculation.



2000 Club Member
I've heard of this before, and had a similar problem. I had a crack appear seemingly out of nowhere in similar conditions. Later, upon careful inspection, I located a previously unnoticed chip in the windshield where the crack originated. This apparently created a weak spot in the windshield that couldn't stand up to the temperature change. Plow jockey's suggestion is a good one, allowing the glass to come to temperature slowly.
In my main line of work, I feel lucky if I get 6 months out of a clear windshield. - lots of rocks thrown by passing trucks on logging roads. These windshields are not too expensive though - I do not put them through my insurance - just pay direct and they are still about 1/2 the cost of my deductible.

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