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Rear bumper - dirt and grime

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Old 03-26-2014, 05:47 AM   #1
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Default Rear bumper - dirt and grime

I am noticing my S6 rear bumper gets exceptionally dirty, much quicker than the rest of the car. After washing it on Sunday, I noticed a fine black film on the entire back end after driving only 20 miles on Monday.

I have driven a SUV for the past 10 years and never noticed anything like that. Is this normal for a lower to the ground car? Is my car putting out black soot from the exhaust?
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Old 03-26-2014, 06:09 AM   #2
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K, welcome aboard! Direct injection cars tend to kick out more particulate matter compared to older engine designs. I notice a similar accumlation on the rear of our A6 (wagon), not so much so on the A4. The rear window on the wagon gets "dusty" very quickly.

You might try an anti-static wax/sealant. I've found that helps a bit.
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Old 03-26-2014, 06:20 AM   #3
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It just gets very dirty. Not sure if it's the direct injection or just the aerodynamics, but you're correct.
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Old 03-26-2014, 06:23 AM   #4
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I've observed this as well, particularly in the wet. I think the aerodynamic design of A6/S6 body is the cause. I don't find that it's soot from the exhaust but mostly just road grime. There must be an eddy current of some sort where, as the air and rain rushes over the car, it pools up to some degree by the rear bumper depositing more dirt than most of the rest of the body.
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Old 03-26-2014, 08:24 AM   #5
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Originally Posted by snagitseven View Post
I've observed this as well, particularly in the wet. I think the aerodynamic design of A6/S6 body is the cause. I don't find that it's soot from the exhaust but mostly just road grime. There must be an eddy current of some sort where, as the air and rain rushes over the car, it pools up to some degree by the rear bumper depositing more dirt than most of the rest of the body.
I agree. I was surprised at how quickly the back of my car got dirty but I found that it was more from the road than the exhaust.
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Old 03-26-2014, 09:09 AM   #6
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I wonder if mud flaps would help...and how bad they might look.
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Old 03-26-2014, 09:27 AM   #7
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This happens on the back of every vehicle. It just shows up more on certain colors, like black. It is simple physics. As you drive, especially at speed, a vacuum is created behind your car that sucks in the dust and grime. Depending on the exact shape of the car, it can be worse in some cases than others.
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Old 03-26-2014, 09:37 AM   #8
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This happens on the back of every vehicle. It just shows up more on certain colors, like black. It is simple physics. As you drive, especially at speed, a vacuum is created behind your car that sucks in the dust and grime. Depending on the exact shape of the car, it can be worse in some cases than others.
The S6 falls under the "worse cases". My M5 didn't trap as much dirt and neither did my previous Cayenne which had a lot of surface are back there.
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Old 03-26-2014, 09:50 AM   #9
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The S6 falls under the "worse cases". My M5 didn't trap as much dirt and neither did my previous Cayenne which had a lot of surface are back there.
I agree. My silver B8 A4 didn't get dirty as quickly as my quartz gray A6 which isn't much darker then the A4. I believe it's the particular body design of the C7 sedans. Probably a design trade off as you would think it was observed in the wind tunnel tests. Maybe the rear end was designed to create a wind force strong enough to help push the car forward improving fuel economy. Kind of like creating it's own racing draft. Then again, probably not.
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Old 03-26-2014, 09:54 AM   #10
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Maybe the rear end was designed to create a wind force strong enough to help push the car forward improving fuel economy. Kind of like creating it's own racing draft. Then again, probably not.
Yeah, probably not.

I agree that the back gets dirty almost immediately. It's especially irksome as the back-up camera becomes essentially useless in anything other than perfect weather conditions.
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