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Moonroof shattered/Exploded

3774 Views 46 Replies 26 Participants Last post by  Tcunningham1979
I was driving to work Friday morning and had just gotten onto I73 in Greensboro. It was 6AM and no one was in front of me as I was on a 2 lane access road getting onto I73. I was driving 70mph. I was maybe 3 miles from home at this point and hear a loud boom followed by a fast flapping sound. I dove towards the shoulder knowing it had to be the moonroof as I could now hear small pieces of glass blowing across the top of the car.

I had it towed to the dealer where I bought it (in Burlington). They are replacing it under warranty for me. This is the 2nd one they received this week with a shattered moonroof. Mine is a 2023 Wilderness with 4800 miles.

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Discussion Starter · #5 ·
It'll be interesting to follow this one. Was it cold outside? Do you have any "gut feel" thoughts on this?
It was mid to upper 40’s outside. The car was not garaged that night either. I honestly feel it was a defect and do not believe any rocks or other debris hit it, but it was very dark out and hard to see. Also, the inner cover was closed, thankfully.

However, the fact they said it was the 2nd one this week made me wonder if it was weather related.
 

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This has been a thing for some time and in multiple makes and models. Here is an article from 2017: Exploding Sunroofs: Danger Overhead

Almost avoided any car with a moonroof because of this, but I enjoy being able to open them. This is definitely an issue that all manufacturers need to work on.
 

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My gut feeling about these things is that tiny rocks can create tiny pits in glass without causing breakage immediately (my windshield has at least a half dozen small pits that you can't see without close examination after feeling them) and then these tiny pits are a weak spot that either thermal cycling or another tiny impact can cause the shattering/cracking. Our windshields are laminated but it appears that the sunroof glass is tempered instead.

Looking at the image of the sunroof glass, it looks like there is an origin for where some of the cracks seem to originate. If there was traffic in the opposite direction a small rock may have been flown your way.

If the glass were laminated it would hang together better but then I suppose there's a chance that a big piece might fly off the car and hit someone else instead of just tiny fragments.
 

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Discussion Starter · #12 ·
My gut feeling about these things is that tiny rocks can create tiny pits in glass without causing breakage immediately (my windshield has at least a half dozen small pits that you can't see without close examination after feeling them) and then these tiny pits are a weak spot that either thermal cycling or another tiny impact can cause the shattering/cracking. Our windshields are laminated but it appears that the sunroof glass is tempered instead.

Looking at the image of the sunroof glass, it looks like there is an origin for where some of the cracks seem to originate. If there was traffic in the opposite direction a small rock may have been flown your way.

If the glass were laminated it would hang together better but then I suppose there's a chance that a big piece might fly off the car and hit someone else instead of just tiny fragments.
The median is huge where I was so I’m thinking it probably wasn’t from cars the other way. It really is rural where it happened, and literally the only car around was right behind me. I really could see it being a rock that hit me yesterday, a week ago, or even a month ago that I didn’t notice. I could definitely see that.
May be that it was defective when made. I really hope it doesn’t happen again nor do I want it to happen to anyone else.

Below is where it happened.

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As a safeguard you can have aftermarket tint film applied to the interior of the replacement sunroof glass so that if it ever shatters again, it won't fragment like that.
 

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GM has had a problem with these for decades as have other manufacturers. The odds of the roof being broken from outside influences such as thrown rocks is very very small. I have seen dozens of them break, never from being hit. I have replaced many of them and had a company attached to one of our dealerships that specialized in installing moonroofs.

Our theory was always either when the roof was installed it was put in with a bind that eventually caused breakage as the body moved in the normal course of driving. Or, when the glass was manufactured there was a weakness that eventually failed because of temperature change and or body movement.

They are easily replaced and I really never had a problem with breaking multiple times on the same vehicle. This is not a Subaru only problem and I am sure they will take good care of you.
 

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All of the other windows in a vehicle are vertical or have some degree of vertical support. A moonroof is horizonal and sees different stresses. Some degree of bending occurs when the car goes over bumps. Not much of course but if there is a defect or some very minor damage to the glass this could act as a stress riser and eventually lead to failure. Just a thought...
Do other windows spontaneously break at the same rate as moonroofs?
 

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I often wondered why they did away with the old metal moonroofs (then called a sunroof.) Moonroofs are not a must have for me, but if I like the car and it is not a big part of an option(s) package I do NOT want I will take one. I have just found I so rarely actually opened mine on cars that had one. However, I am an A/C addict and do not like sun on my head or the wind noise. I did like the big panaramic sunroof on our MB Sport Coupe.
 

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Odd, I never got the memo on this one. So steel = “sunroof”, glass = “moonroof”?
Frankly I do not know, but I remember when the terminology appeared to change. In the 60's and 70's (at least with German and some other European cars) they were sunroofs, and most of them were sliding steel with cranks to open them (some had to be pulled back), even on a lowly VW Bug after the early 60s (early 60s Beetles and other Euro-cars often had canvas). The Citroen 2CV has a great big full retractable canvas roof. We used to ride around with our heads out of the VW Beetle sunroof like tank commanders by sitting on the front seatbacks. Also keep in mind that back then AC was often an option and sometime even a bolt-in dealer or after-market option and not universal like climate control.

The after-market offered bolt-in and tilting glass or plexiglass 'moonroofs' that did not actually fully open, but some did allow you to pull the panel out. Kits were common in JCWhitney catalogs. Back in the 70s when there was a roll-over safety campaign against convertibles, US cars were lucky to even get a T-top, although T-tops got big with GMs Camaros and Trans-Ams. It seemed that moonroofs really became the terminology when US auto companies began to offer them. Maybe it was just a romantic term like 'Fine Corinthian Leather' by Chrysler on its Cordoba. But I used mine almost exclusively afternoon or evening.

The crank open metal ones of the old days did not cost you much headroom. I never had a metal one leak, but then my later glass ones never leaked either, but that was because I had learned to keep the drain lines clean.

Actually if a current Outback was time-teleported back to that time, it would seem like it was from the Starship Enterprise. We have come a long way.
 
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