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Old 08-13-2019, 09:16 AM
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Zooks527 Zooks527 is offline
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Brown smoke?

Sure, it's a Honda not an E90 BMW, but I'll plead general older car knowledge instead of OT, assuming the forum is no longer as strongly moderated in the past and hoping I've got a bit of latitude from post count.

Saw this on the highway this morning. I had been behind this guy for several miles, with not a sign of an issue. The car in front of me started to accelerate, kicked out a short burst of brown smoke after a few seconds, then slowed down and pulled over to the breakdown lane. He was coming off speed pretty quickly as he moved over (my speed is shown in the bottom center of the image).

I know what black, blue, and white smoke out the exhaust mean, but I haven't seen brown before, especially in a single short burst. Any ideas on the possible cause?

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Last edited by Zooks527; 08-13-2019 at 09:18 AM.
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Old 08-13-2019, 04:39 PM
gbalthrop gbalthrop is online now
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Quote:
Originally Posted by Zooks527 View Post
...I know what black, blue, and white smoke out the exhaust mean, but I haven't seen brown before, especially in a single short burst. Any ideas on the possible cause?
SWAG: Backfire blew rust out of muffler/resonator, particularly if he accelerated hard to get ahead of you and then let off gas suddenly. Did you notice any unusual exhaust noise (from HIS car hopefully ;-) when you passed him?

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Old 08-13-2019, 05:50 PM
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Zooks527 Zooks527 is offline
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Originally Posted by gbalthrop View Post
SWAG: Backfire blew rust out of muffler/resonator, particularly if he accelerated hard to get ahead of you and then let off gas suddenly. Did you notice any unusual exhaust noise (from HIS car hopefully ;-) when you passed him?
I was thinking rust out of the pipe somehow, but not sure why it would go then. He had been in front of me (with a lane change or two) for a while, and had done a few accelerations more active than that one. Whatever it was, it was either making a ton of noise inside his car (don't think so) or there was some sudden performance change after that puff. He headed for the shoulder pretty quick once the car next to him cleared out.

Personally didn't hear anything, but I will confess to having the radio cranked up quite a bit.
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Old 08-13-2019, 08:03 PM
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Did you smell anything unusual afterward? My first guess would be carbon/soot: It can look brown when it's old accumulation being blown out, rather than a by-product of poor combustion. (I've seen this color in the rear-view mirror on occasion if I go too long between Italian tune-ups.)

As to why he pulled over, I could speculate that the source of said carbon was ingestion of a nice-sized chunk of coke dislodged from an intake valve. I'll bet that would sound interesting inside a high-strung little Honda four-banger.
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Old 08-14-2019, 05:15 AM
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Zooks527 Zooks527 is offline
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Originally Posted by Zeichen311 View Post
Did you smell anything unusual afterward? My first guess would be carbon/soot: It can look brown when it's old accumulation being blown out, rather than a by-product of poor combustion. (I've seen this color in the rear-view mirror on occasion if I go too long between Italian tune-ups.)
I was driving my 2005 Tacoma with 230,000 miles on it at the time. Tell me when I don't smell something unusual. But no, nothing untoward. Didn't notice any smell at all. Interesting comment on the soot - my very first thought when I saw it was "Honda's putting diesels in those?". Reminded me of what used to come out of a friend's early-80s diesel rabbit back in the day.

Quote:
Originally Posted by Zeichen311 View Post
As to why he pulled over, I could speculate that the source of said carbon was ingestion of a nice-sized chunk of coke dislodged from an intake valve. I'll bet that would sound interesting inside a high-strung little Honda four-banger.
I imagine that would cause quite a thunkin' !
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