Heat related dent in black roof?

[Pamlico]

Over on Roadfly there is a thread concerning the apperance of a dent or crease appearing in some Minis with black roofs. The dent runs in a front to back direction and appears only when the car has been sitting in full sun for a number of hours. It disappears when the roof cools down.

Apparently not everyone with a black roof experiences this, but there were several postings from owners with the same issue.

One concern I'd have is that the repeated flexing of the metal would eventually lead to cracks in the paint.

Has anyone with a black roof Mini seen this problem? It doesn't seem to be an issue when the sunroof is installed.

[R1]

I've noticed this on my last MINI and this new one.

I also noticed it on nearly all black roofed MINI's I've seen (including ones at the Silverstone MIN2 meet recently), only after being in hot sunshine all day.

As soon as it rains or cools down, it goes without a trace!!

Weird!!!

Any thoughts MiniGuy?

[BruceK]

Well, if it's that common someone should be able to get a picture of it to help show others what it looks like.

[R1]

Here is the link to the photos page. It is hard to photo though!
http://forums.roadfly.org/mini/forum...=577647&page=1

[MINIAC]

From the Roadfly thread:


Photo #1: (You can see the distortion in the reflection of the roof of the house)


Photo #2: (You can see what I meant by a crease, from front to rear)


Photo #3: (Pretty apparent here)

[click 'em Dano]

[Ady]

Afriend at work came to me for a chat today and this is one of the things he mentioned. It was the first time i had heard about it from him and then i see this on the forum, he has a Black MINI one and same symptoms it comes and goes with the heat. Lucky for me i will be having a sunroof in my black roof so i shouldn't get this

Ady (R50)

[AidenL]

Good reason to go with a white roof !

[EBMCS03]

Yikes!! is this cuz how black absorbes the heat from the sun? No one heard of this on white roof right??

[cooper4us]

I just see a lot of people panicking, much speculation and little technical explanations here.

Can anyone explain what are the construction and material differences between the black and white MINI roofs?????? (Aide from the obvious color difference).

I tend to believe the roofs of these cars are all made the SAME and the "Problem" could even be manifesting itself on white roof cars as well.

Sorry but I fail to see the big deal on this mysterious "dimple problem". What are they going to do? bring a chainsaw and chop off the roof of your car and put a new one?

I am still very glad that I chose the black roof over the white roof. Some people have too much time in their hands.

Peace!

[sjbartnik]

Quote:

Can anyone explain what are the construction and material differences between the black and white MINI roofs?????? (Aide from the obvious color difference).

I tend to believe the roofs of these cars are all made the SAME and the "Problem" could even be manifesting itself on white roof cars as well.

Of course the roofs (rooves?) are made the same. However a roof painted black is going to absorb all the heat and light energy that falls on it during a day out in the sun and get quite hot. This heat is apparently what is causing the roof metal to expand and dimple.

A roof painted white is going to reflect most of the heat and light energy and so shouldn't get as hot. The problem hasn't been seen (yet) on a white roof.

Also the problem has not yet been seen on sunroof cars. I suspect this may be because the gap between the sunroof and metal roof allows for some metal expansion or perhaps the extra bracing in the roof to make up the structural rigidity that the sunroof takes out keeps the roof from dimpling.

I guess the worry is that over time this continued flexing of the roof will cause the paint to crack. Time will tell I suppose.

[PghArch]

To answer part of the question, it is certainly believable that the black color could allow the roof surface to become that much hotter than the white on a sunny day. I would guess that a comparison of well waxed roofs would find that the black absorbs anywhere from 2-5x as much direct radiation.

The slight buckling looks to be the result of the metal roof surface having temperature expansion forces in excess of any flexure available relative to it's attachement to the frame. A large relatively flat metal sheet like that will move pretty far in the temperature range from -40f to 140f that it is likely to be able to experience.

It is quite possible that the dimple is an intentionally left "weaker" spot on the roof to allow for release of these excess forces. Otherwise they would be working to spring the roof piece loose at the edges. Overall, I would agree that the main concern is likely the effect that flexure has on the paint. However the paint is probably also more resistant to cracking at high temperatures so this behavior may be within it's elastic limit.

All just guesses as to the causes and effects. The biggest problem in practice may be convincing folks that there isn't anything really wrong with your beauty ;-) .

[cooper4us]

I appreciate the responses. Absolutely, a black roof (Even a black or dark coloreed car) will always absorb more light and heat than a comparable white/lighter colored car. As far as how well the black paint integrity will be maintained under these circumstances, time will only tell but I suspect that given the "Flexible" nature of most automotive paint finishes today, this will not represent a serious concern years down the road. A family acquitance has a 2002 VW Golf all Jet Black and the car is a toaster oven when left parked under the sun. At least the interior is beige/tan so it helps a bit.

I have a light colored car with a light interior and it stills gets mighty hot inside.

I have never paid attention to the metal roofs in cars in hot climates. Maybe the MINI is not the only one suffering from this problem after all.


Will continue to monitor this topic....

[R1]

The roof thing is a genuine phenomenon!! I first noticed this looking out onto the car from an upstairs window on a hot sunny afternoon (which is rare in the UK these days!!)

I have since noticed that my MINI isn't the only one either. I would go as far as to say it will affect ALL black roofed cars.

I am a qualified vehicle body builder and I know the complexities of roof design.
I have not been overly worried by this but it is a "design" fault though!!

Don't ask me how to overcome it, because if they put anything like strengthening panels/struts or material in the roof then it will probably just move the problem!!

By the way. Have you noticed that most cars these days have two joins and or plastic strips running down both sides of the roof. Expansion strips?

I should have had the sun roof!!



Bugger!! Could this qualify as my first fault??

[sjbartnik]

Quote:

Originally posted by R1

By the way. Have you noticed that most cars these days have two joins and or plastic strips running down both sides of the roof. Expansion strips?

[/b]

Rain gutters
These are the modern equivalent of old-style rain gutters. The old-style went bye-bye due to more stringent aerodynamic controls. Unfortunately the new style rain gutters don't prevent water from falling into the car when you open the door like the old style do.

Perhaps they also serve as space for expansion.

[R1]

Quote:

Originally posted by sjbartnik

Unfortunately the new style rain gutters don't prevent water from falling into the car when you open the door like the old style do.

A bit like the MINI's then!