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Heat and Windshield Breakage

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The nice weather of summer can be great for barbecues, pool parties and more, but it can be hard on your windshield. Your windshield is more likely to crack—and cracks are more likely to spread—when the temperature changes. Temperature changes cause glass to expand and contract, which can make your windshield a bit more fragile. Likewise, many of us are on the road more in the summer as we travel on vacations, to visit family or just make runs to the local pool. All of this leads to an increase in broken windshields that will need to be replaced.

Hot Temperatures Stress Windshields

Temperatures swings can put extra stress on the windshield and make it more prone to breaks. Likewise, if the glass cools too quickly this also can cause stress on the windshield. Experts recommend that you take your time in cooling your vehicle’s interior (and therefore the glass) so that cracks are less likely to expand. This might mean turning on your air conditioner to low at first, instead of going full-steam at once when you turn on your car. Also, many say you should be careful about slamming your doors too hard, as even this type of jarring can lead to increased stress on the glass.

More Travel Means More Broken Windshields

While the sun may stress your windshield, summer time is often a time for people to de-stress themselves. More vacations mean more road travel, and more road travel means more broken windshields. Last August, U.S. road travel was up 3.4 percent over the previous year—with a total of nearly 285 billion miles driven by vehicles in the United States. So as you plan your summer road trips, keep in mind that anytime you are on the road, the probability of a broken windshield increases. Combine this with the above stress issue, and you have a recipe for a rising number of broken windshields.

Watch Your Windshield for Damage

You can’t control the temperature, so what should you do? First, keep a close watch on your windshield. Inspect it often. If you get a crack or a chip in your windshield, the hot temperatures can cause the chip or crack to expand more quickly.

As soon as you see a chip or crack appear in the summer, you will want to get it fixed. If you do so quickly enough, it can sometimes be repaired (without having to have the entire windshield replaced). In a repair, a special kind of resin is injected into the break to keep the crack or chip from spreading. The crack or chip likely will still be visible after repaired, but this will at least save your windshield—which is good for both the environment and your pocketbook.

However, if the crack or chip expands beyond the point of repair, the entire windshield will need to be replaced. This is why it’s important to watch the windshield closely and ensure that you are aware of any chips or cracks as soon as they appear, and contact an auto glass shop quickly to check out the damage.

Be Cautious

If the windshield does break beyond repair, you will want to account for this when it is replaced. Many urethanes (the substance used to bond a windshield to the vehicle) can only be used under certain temperatures and humidity conditions. You will want to ask the technician doing the work if the urethane being used is appropriate for the hot weather, or find out if there is an indoor location at which the work can be completed.

Additionally, you’ll want to pay attention to the Safe Drive Away Time (SDAT) (also known as Minimum Drive Away Time or MDAT)—the time that your vehicle needs to allow the adhesive to cure before it can be driven after a windshield replacement. The MDAT can vary depending on the outside humidity and temperature, and your technician should provide details about this to you. (Conversely, if you are getting your windshield replaced on an extremely cold day, this can affect the SDAT as well. Any extreme temperatures, hot or cold, need to be accounted for—and you should ask your technician for details on the type of urethane that is used.)

The company you choose to replace your windshield may even ask you to come into the shop or your garage can be used so that the work can be completed indoors (and at an appropriate temperature). If an indoor bay, garage or shop isn’t available, the shop may simply suggest you wait another day or two, until the weather conditions change.

What Now?

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If you do find yourself in need of a summer windshield repair or replacement (or anytime for that matter), there are many quality auto glass businesses out there available to replace your windshield. has affiliate shops all over the United States ready to replace your glass when needed. We let you compare instant price quotes from the hops in your area and book with the shop that’s right for you. You will want to make sure you get the best deal, to allow you more money for those summer vacations.

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Penny Stacey

Penny Stacey serves as the communications manager for Key’s association clients. Her job is to augment communications efforts as needed or requested by the association. She currently edits four association newsletters, writes press releases and story pitches for these clients. She also helps with research as requested. Penny has been part of the Key Media & Research team for 17 years, and has served as an editor for a number of Key publications, e-newsletters and websites. She graduated from Mary Washington College with a bachelor’s degree in both English and American Studies. She works part-time now while raising her two young boys. Find out more about Penny on Linkedin.

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28 Responses

  1. I’ve got an older car and the windshield recently cracked without any sudden impact. I think the biggest cause of it cracking was the heat and the fact that it’s about 40 years old. It’s a rather curious situation and I’ve never had it happen before, so, doing as you recommend and contacting a professional about what to do could be helpful because finding out whether I should replace it so it doesn’t happen again or just repair it would be good to know.

    1. Hi James, there could be several reasons why this is happening, or a combination thereof. First, inspect the glass thoroughly before removal to ensure there is no pre-existing damage. Second, if the glass gas been sitting in direct sunlight, it might be best to move it to shade before removal to let it come down to a moderate temperature prior to handling. Third, ensure that the removal process is being performed correctly with the proper tools. Lastly, be sure the glass is being stored properly in a windshield rack.

  2. Does a windshield need to be warmed up slowly from 10 degrees before a chip can be repaired or should it be done cold?

    1. Hi Kadyn,

      Windshield repair technicians may use different tools, techniques and resins to fill chips so the answer to this question may vary depending on the tech’s experience level and the equipment they use.

  3. I have a Mazda CX5 still under warrenty. The other morning I wet out to drive the vhicle and there was a crack in the windsreen. The vehicle is parked under my house in a secure estate so it would not have been vandalised. It was particularly hot the previous day in the carport. Could the heat have done it? I reported this incident to Mazda Technical and the dealer but typically they are both trying to sidestep the issue.

    1. Hi Tom,

      Yes- it is possible that the heat may have caused the crack to occur “spontaneously”. Look at the damage closely and see if there is any place that looks like it could have been impacted by an object. If so, it wouldn’t be considered a “spontaneous” break. It’s possible that there was a very small impact at some point that went undetected, but spread due to the temperature.

  4. I have a question. I just bought a 2017 F150 and within 2 weeks a rock hit my WS. Within 12 minutes it traveled the length of the WS & had to be replaced. After 3 months of owning it, I got 2 more rock chips and repaired them. Then after 5 months, another chip happened and when I went to repair it, it cracked the full length. Now I’m getting a 2nd windshield installed in only 6 months of owning this truck. There has got to be something going on with auto glass quality? I’ve driven trucks since the 70’s and lived in TX. and never had this much grief. I’m really sick of it and even my insurance company is getting alarmed at 2 windshields and multiply repairs within 6 months. What the heck is going on with auto glass? Thanks.

    1. Hi Joy,

      I can certainly appreciate your frustration! To start, when you had the first windshield replaced, was it replaced with an OEM quality windshield? Replacing with an aftermarket windshield could raise questions of quality. Second, have you noticed more road work on the roads you’re travelling? More inclamate weather, or anything else that could cause more debris on the road? Even extreme fluctuating temperatures could have an effect on windshields. Lastly, I would say that if you haven’t had to replace a windshield since the 70’s then, statistically, things are catching up with you since the average driver replaces a windshield every 8 years.
      Hopefully this is the end of your streak for a while!

  5. Penny, thanks for your comment about how you should replace your windshield when the crack spreads. I like how you said that you should always hire a professional to do make any repairs or replacements. My husband and I are looking into getting our car’s windshield replaced because it has a large crack in it.

  6. Can heat cause the windshield to become brittle? I have a COVERCRAFT UVS100 Custom Sunscreen that’s made specifically for my car. It has Triple Laminate Construction and a Foam core center that acts as an insulator. I noticed that the side facing the windshield gets very hot here in Houston, TX. Could this heat harm the windshield? Should I not use this sunscreen on my 2017 Infiniti Q60?

    1. Hi Mark,

      This is a great question! Glass is a very unique material in that is is really neither a liquid nor a solid because it exhibits characteristics of each state. There is no exact freezing or melting point. In a cooled state, molecules do not move. They are randomly configured, but they will not crystallize. In a warmed state, molecules will move about freely. The higher the temperature, the greater the movement.

      So your windshield actually becomes less brittle as it heats up. In theory, if it become hot enough (HIGHLY unlikely) it would sag and cave in rather than break. What you need to be cautious of are temperature differences which cause rapid heating or cooling. Let’s say that the sunscreen causes your windshield to heat up to 120 degrees when the outside air temperature is 20 degrees. This could be cause for concern. Or if you immediately blasted your air conditioning on defrost mode after using the sunscreen in the summer time.

  7. Hi, I recently just bought a used car from a dealership. Prior to buying the vehicle, there was a repair that had to be done to the windshield. Now it’s been two months, and the windshield has to be repaired again, without the dealer paying for it. I’m wondering what may have caused the windshield to crack. It appears that it happened on one rather warm day, and as I warmed up my car this morning, I noticed the crack extended.

    1. Hi Vanessa,

      Thanks for reaching out regarding your frequent windshield replacements. You may want to check out this recent Q&A with our Glass Detective.
      Basically, there’s always a cause, no matter how random it appears. You may want to figure out what has been used as replacement glass the last 2 times- for example, is it OEM glass, or is it aftermarket glass from a little known manufacturer? One option could be skipping the dealership and speaking directly with a well known and reputable auto glass replacement shop in your area.

  8. I didn’t realize that exposing your cracked windshield to the sun could cause the crack to expand, or that blasting the AC when you get in could do that. I’ve noticed that a small crack in my windshield got a lot bigger yesterday and I couldn’t figure out why. This explains it since I park in the sun, so now I’ll probably have to replace my windshield.

  9. I recently purchased a used (2015) vehicle. Before I was able to take it home the dealership realized that the front windshield was tinted but not at an acceptable tint according to Ohio laws. They removed the tint. I have been driving the car for about a month. I had her parked outside on the driveway in the sun while I cleaned out the garage. When I went to pull her back in the front windshield was cracked. I have had impact cracks and chips on other vehicles. This was not like those. Nothing hit this window to cause this kind of crack. And I drove her the last couple of days in the same heat conditions. Is it possible that removal of this tint could cause a window to break? This crack starts low in the front about 3/4 of the way in from the drivers side. It flexes up into one solid perfect line. Bazaar. It just seems like a thermal crack shouldn’t occur, and there are no inclusions, so an imperfection of some kind maybe? I am just trying to make sense of it cause most windows are tougher than this. I just wish to rule out if the tinting could have caused a flaw or weakness in the window. Any help would be great! Thanks.

    1. Terri, tinting and removing tint from glass should not have any effect on the integrity of the glass. I think it’s safe to rule out this possibility.

  10. Thanks for sharing with us that if the glass cools quickly, that can give rise to windshield damage. Since cool months are already upon us, that is a good reminder that will move us to think of proper precautionary measures to make the windshield resistant to that. Yet in case the windshield or any part of the front glass of the car will break down due to extreme temperature, we are open to seeking the service of those in the repair business.

  11. Hello,

    I have a 1940 pontiac with a two piece windshield. The drivers side has a small crack and I was looking into replacing the glass with “legal” gray or OEM style green tint. Th e existing glass does not leak. I wanted to see an improvement in lessening the heat transmitted through this existing clear glass. However, the 150 for the glass, 150 for a new gasket, 300 for install does make the option of replacing cost prohibitive for me at this time. I have decided to just put a light window film such as 3M Crystalline for the immediate future. If I read one of your replies correctly, putting the film on will have no negative impact on the glass, or am I wrong?

    Thanks For You Help

    1. Hi Robert,

      Thanks for the question! Unfortunately, applying window film to the windshield is not a good option. There are very few instances when it is legal to apply window film to a windshield, so check with your local and state laws before moving forward.

  12. I have a tenant with a 2018 Mercedes. He parked it in the garage and says the heat of the garage broke his windshield. He says it is not covered under warranty or insurance and that it did not have any cracks or chips. Could the heat of the garage break a windshield on such an expensive vehicle?

    1. Hi Sandy,

      You didn’t indicate how hot the garage gets. But assuming it’s no hotter than an average garage, no, this would not cause a windshield to crack. Heat by itself will not cause glass to break, but drastic temperature changes can. For example, driving out of a hot garage and immediately blasting cold AC onto the windshield would put a large amount of thermal stress on the glass.

  13. My rear view mirror fell off my windshield. I was told by a coworker that I would have to wait until cooler weather to put it back on as we live in Florida and the extreme heat combined with the glue heating up the windshield could cause my windshield to crack. Is this true? I can’t find anything online supporting this theory.

    1. Hi Angela,
      Thanks for the question! Glass shops are pros at reattaching rearview mirrors and if you have any doubts, you should take your car into a shop to have this job done. The main concern will be more about making sure the adhesive sets properly so that the mirror stays in place. Cracking is possible, but very unlikely. Re-attaching the mirror should be done in the shade, a temperature controlled shop, or at night, ideally with an ambient temperature between 50 and 75 degrees Fahrenheit. It also needs to be done in when moisture levels are low (no rain). The mount and the windshield will need to be prepped thoroughly to ensure the mirror stays intact for a long time to come. Good luck!

    1. Hi j.atwater,
      We do not have these statistics. If you have a resource for this information, please let us know!

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