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      07-01-2009, 03:47 PM   #1
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Catless exhaust system = yellow stuff?

I saw in another thread that a few people with catless exhaust systems get a yellowish residue on the back of their cars.

Can anyone elaborate on this? What is it? How hard is it to clean off? Is it bad for the paint? How long does it take before you need to wash it off, ie. is the build-up noticeable after a few days or a few weeks? Where exactly does it accumulate? Is it underneath the rear bumper or around the back of it also? Thanks!
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      07-01-2009, 03:59 PM   #2
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      07-01-2009, 04:52 PM   #3
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Quote:
Originally Posted by ///M Pow3r View Post
I saw in another thread that a few people with catless exhaust systems get a yellowish residue on the back of their cars.

Can anyone elaborate on this? What is it? How hard is it to clean off? Is it bad for the paint? How long does it take before you need to wash it off, ie. is the build-up noticeable after a few days or a few weeks? Where exactly does it accumulate? Is it underneath the rear bumper or around the back of it also? Thanks!
Probably the exhaust heat from the exhaust itself caused that. You can't clean it off since it's basically burned. You probably should get a bumper shield that protects those areas from the extreme heat.
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      07-01-2009, 05:25 PM   #4
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I don't have a catless exhaust, but I saw another guy say his local carwash used some special spray to wash it off. I wonder what it is
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      07-01-2009, 05:35 PM   #5
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well your cats are a place that offers an environment for certain chemical reactions to happen. the cats themselves have chemicals that allow reaction with the toxic chemicals coming into them, to make them less toxic.

i can imagine if there's no cats -> there's no chemicals to tame down what enters them -> that yellow stuff is some nasty ass toxic chemicals. dont touch that shit
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      07-01-2009, 06:04 PM   #6
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I dont think there is any noticeable increase in heat from removing cats. It is probably the exhaust gases that are dirtier and stick to the bumper. i wash my rear bumper often to avoid the yellowing, but i hope someone can chime in on a solution to clean it when it does turn yellow.
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      07-01-2009, 06:09 PM   #7
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maybe clearbra the area around the exhaust tips...
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      07-01-2009, 06:23 PM   #8
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Catless

on space grey no yellow 3+ months
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      07-01-2009, 06:26 PM   #9
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look closely...i hadnt even noticed on my white until i saw this post...its not too bad but if you let it build up it is very tough to get off (trust me)
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      07-01-2009, 07:39 PM   #10
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So what chemical/method do you use/do to get the yellow stuff off?
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      07-01-2009, 08:41 PM   #11
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usually with soap and water it comes off with alittle knuckle behind it...believe or not i have also tried the bug remover and it works great as well...i am not sure if its the best for the paint but it works
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      07-01-2009, 11:54 PM   #12
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Quote:
Originally Posted by !Xoible View Post
well your cats are a place that offers an environment for certain chemical reactions to happen. the cats themselves have chemicals that allow reaction with the toxic chemicals coming into them, to make them less toxic.

i can imagine if there's no cats -> there's no chemicals to tame down what enters them -> that yellow stuff is some nasty ass toxic chemicals. dont touch that shit
Haha yeah I'm pretty sure it's some kind of toxic crap since it's pretty much unfiltered through cats, but I was wondering if anyone knew exactly.
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      07-01-2009, 11:55 PM   #13
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Quote:
Originally Posted by m34jlp View Post
look closely...i hadnt even noticed on my white until i saw this post...its not too bad but if you let it build up it is very tough to get off (trust me)
Is it a kind of film? Or a stain? Would you mind posting a pic, or can you describe exactly where it built up?
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      07-02-2009, 03:12 AM   #14
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I don't see any residue on mine. Albeit I have a VRS diffuser, and I do not notice it on there.

I have a yellowish tint on my exhaust tips. A little polish will take that out.
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      07-02-2009, 03:38 PM   #15
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Quote:
Originally Posted by ///M Pow3r View Post
Is it a kind of film? Or a stain? Would you mind posting a pic, or can you describe exactly where it built up?
will do when it builds up again i'll snap a pic
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      07-02-2009, 04:01 PM   #16
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Quote:
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will do when it builds up again i'll snap a pic
Cool thanks
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      07-02-2009, 04:41 PM   #17
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nothing happens to your car, i didnt wash it for over a month. im catless + supercharged. you just have to use soap/water.
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      07-02-2009, 04:48 PM   #18
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Quote:
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nothing happens to your car, i didnt wash it for over a month. im catless + supercharged. you just have to use soap/water.
Good to know, thanks
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      07-02-2009, 05:16 PM   #19
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It only happened to me the first week. Then it never happened again.
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      07-02-2009, 07:37 PM   #20
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Quote:
Originally Posted by m34jlp View Post
I dont think there is any noticeable increase in heat from removing cats. It is probably the exhaust gases that are dirtier and stick to the bumper. i wash my rear bumper often to avoid the yellowing, but i hope someone can chime in on a solution to clean it when it does turn yellow.
+1

The yellow builds up over time. On a white car it shows a lot and it's the entire back that builds the yellow but it's most evident on the bumper since it's right next to the exhaust.

It was me that posted about my local car wash cleaning it WAY easier than when I tried it. Next time I'll ask them what they used.

It probably only shows on the AW only. No big deal and NO it's not extra heat burning your paint ! It takes about a month of buildup before it gets really bad.
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      07-02-2009, 08:01 PM   #21
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Just fyi, the cats add heat that burns off unburned gas and changes the chemical makeup of the exhaust. Removing the cats allows more of the engine residue to excape out the exhaust. That residue is probably what you're seeing. It's NOT burning the paint, but you do need to clean it off regularly.

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      07-02-2009, 09:37 PM   #22
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I think I posted this somewhere else, but a mild solvent works well (acetone applied lightly takes it right off), or if the car has a good layer of wax on it most liquid cleaning polishes will take it right off, while at the same time protecting it.

For the tips any good metal polisher will give those things a brand new look with a little elbow grease - I wish I had the stuff in front of me and I can't remember the name of it off the top of my head but there is one out there I started using my friend turned me onto that protects specifically against tars and carbon residues, so its perfect for the exhaust (just requires much less work to get the tips that brilliant shine afterwards)
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