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I was sitting in my car while it was running. Outside temperature maybe 90° and A/C was on coldest setting at about half strength. It was rainy and muggy outside, no direct sunlight. Nobody was around my car and I was sitting inside it on my phone to wait for a friend to come outside. Suddenly I hear something like a gunshot and duck. After I get over the shock, I get out of the car and look around for what caused it. Nothing. I turn to look at my car and it looks like my roof had a bomb thrown at it from the inside. How much to fix this? Or how expensive could it get? What could have caused it?
I had to drive home and glass was falling out of the screen and into the car as well as bigger chunks were flying off behind me and into the road so I broke off anything that was fragile and vaccumed. And I ended up taping it off to keep out the rain.
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This was an occasional problem a decade ago and then there were none until your post today - mainly MY08 models from memory and my opinion it was confined to a few production batches compromised by residual high internal stresses from the glass manufacturing process intended to result in safe fragmenting of the glass in an accident situation rather than sharp-edged shards to minimise possible occupant injury.

My assessment of the cause is the temperature differential between the cod interior of the car and hot glass from the heat of the sun generating high stress levels in the glass sufficient to cause it to fragment.

This was a common problem in our climate in the early 2000's however the glass manufacturers have found a cure as it is rarely heard of now.
 

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An exploding sunroof isn't a common fault but I gave a possible explanation to another member whose sunroof exploded on a hot day whilst driving. It will be quite an expensive repair because a lot of work is needed to remove, replace and get it aligned with seals so there's no leaks afterwards. It's really V.W main dealer EOS roof trained technician work, not a repair by the roadside windshield repair company. If you have comprehensive glass insurance that covers the sunroof, you will get your moneys worth as the labor cost for this specialist work is huge. If your sliding sunshade is in poor condition, this is the time to get it replaced.

The heat tempered glass can withstand temperatures up to 500-600 Centigrade and it isn't heat per-se that causes the failure. The polyurethane adhesive used to fix the glass has some flexibility when hot and its frame is held in rubber seals. Differential expansion and changing dimensions shouldn't be an issue.

The first most likely event is a small stone has dropped on the glass and chipped the surface. This might be hardly noticeable but causes a weakness sufficient for heat tempered glass to fail spectacularly. They use very thin glass.

The second and (I think) most plausible explanation is the glass can get so hot you can't touch it. This is fine until the air con blower is switched on and the inside surface of the glass gets hit by a blast of cold air concentrated in two spots. I did some cabin smoke tests to confirm cold air from the front vents lands just left and right of center towards the front of the sunroof glass when its closed.

If you look at the design of the front air vents they have a tendency to 'roll up' naturally and shoot air upwards against the sunroof glass. When I sit in my EOS on a hot day, I always roll the windows down or open the sunroof before putting on the aircon and then at the slower speeds until the car gets moving. I've looked at the front vents and I'm going to find a way to restrict their upwards angle.

I see in your photos that the sunshade is closed which would help keep some cold air off the glass, but was it closed when the glass exploded?
 

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I was sitting in my car while it was running. Outside temperature maybe 90° and A/C was on coldest setting at about half strength. It was rainy and muggy outside, no direct sunlight. Nobody was around my car and I was sitting inside it on my phone to wait for a friend to come outside. Suddenly I hear something like a gunshot and duck. After I get over the shock, I get out of the car and look around for what caused it. Nothing. I turn to look at my car and it looks like my roof had a bomb thrown at it from the inside. How much to fix this? Or how expensive could it get? What could have caused it?
I had to drive home and glass was falling out of the screen and into the car as well as bigger chunks were flying off behind me and into the road so I broke off anything that was fragile and vaccumed. And I ended up taping it off to keep out the rain. View attachment 22604 View attachment 22605
View attachment 22607 View attachment 22608
 

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Ok sooo I know exactly what your talking about I was driving at 10pm at night on I95 and all a sudden I thought I was getting shot at I was soo scared....well just like you no u rock no underpasses I went under!!!!! It just exploded on me soo scary. So I called VW and acted As if they never heard of this happening and quoted me 12 grand to fix....I said go F####yourself. I ended up finding this random guy from autozone while I was there n he literally got my glass for 500 dollars and fixed it.... only thing is VW does have there specifically owned tools to even take sunroom off. I guess the found someone to borrow that special tool. But long story your not crazy it happen to me and do not pay 1200 grand or anything close to that as they will quote you on.
 

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I found that special alignment tool on Fleabay for < £50 and snapped it up! :) The main thing for your cheap sunroof repair is to wait for torrential rain and see if it leaks because most of the work to replace the sunroof glass is getting the sunroof frame seals and guides to align so it doesn't leak afterwards.

If the seals don't align, water will pour into the drains which aren't there to save faulty seals. If they didn't get the sunroof track rails correctly aligned, the sunroof motor or Bowden cables may fail through excessive friction and that will cost a lot more to fix.
 
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