# Is your tailpipe black inside? **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** yukon, gmc\ **Created:** [January 29, 2019, 8:40am UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523 "2019-01-29T08:40:13Z")\ **Posts on this page:** 12\ **Page:** 2
**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\ **Post date:** [January 30, 2019, 12:24pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/21 "2019-01-30T12:24:30Z")
> [@Honda\_Blackbird](#): > > I can also promise 14.7:1 will not pass the “white glove test” on the inside of any exhaust component. This is simply the normal byproduct of combustion. > > So unless your motor oil stays clean and a “see thru” golden color and looks unused for the entire oil change interval, you too have black soot in your exhaust. That really is the long and short of it… > > Perfectly normal. Thanks, Blackbird! That’s information from **a qualified professional**. I can take that information to the bank and advise @John111 to trust in it, too. _ **CSA** _ 🌴🕶🌴 ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [January 30, 2019, 2:46pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/22 "2019-01-30T14:46:41Z")
The soot issue is worse with direct injection, these engines start pushing the particulates limits on the pollution regs. ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [January 30, 2019, 2:57pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/23 "2019-01-30T14:57:11Z")
> [@texases](#): > > soot issue is worse with direct injection That may explain why my wife’s DI car has such dirty exhaust tips. The other 2 are not DI engines. ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [January 30, 2019, 3:00pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/24 "2019-01-30T15:00:51Z")
Whenever I walk behind either truck and pay any attention to the exhaust pipe it is quite obvious that there is no carbon soot or anything else in the tail pipe. It just a reddish brown that appears to be a light coat of rust. ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [January 30, 2019, 4:35pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/25 "2019-01-30T16:35:10Z")
> [@Honda\_Blackbird](#): > > Burning fossil fuel in any engine creates soot… this is what turns your oil black. So exhaust pipes, mufflers etc will have some soot in them, none are exempt from this. The cat converter burns up some soot, yes? It seems every pre-cat vehicle’s pipe is black or grey with lead. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [January 30, 2019, 4:41pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/26 "2019-01-30T16:41:38Z")
Nope, the cat doesn’t burn soot. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [January 30, 2019, 5:20pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/27 "2019-01-30T17:20:42Z")
Black soot in the tailpipe is caused during a cold start where the computer is in the open loop mode and the A/F mixture is rich. The carbon created during combustion mixes with water created during combustion which then coats the inside of the tailpipe with soot. Tester ---
**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\ **Post date:** [January 30, 2019, 6:23pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/28 "2019-01-30T18:23:13Z")
Another professional, @Tester, weighs in… Sounds quite plausible. Thanks, I’ll go with that, too. All this talk about AFR is accurate **after** the vehicle gets up to operating temperature. _ **CSA** _ 🌴🕶🌴 ---
**Author:** ![NYBo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nybo/32/17281_2.png) [@NYBo](https://community.cartalk.com/u/NYBo)\ **Post date:** [January 31, 2019, 3:30am UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/29 "2019-01-31T03:30:58Z")
A bigger question: Does your chewing gum lose its flavor on the bedpost over night? (Apologies to the OP, the other responders, and Lonnie Donegan) ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [January 31, 2019, 3:40am UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/30 "2019-01-31T03:40:00Z")
For some reason my smaller engine 4 banger econobox car’s (going back to the 70’s) tailpipes have always looked a little black, and feel a little oily. my v8 truck’s tailpipe has always looked clean, if anything a little light rust colored. cars: fuel injected. truck: carb’d ---
**Author:** ![John111](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/john111/32/14752_2.png) [@John111](https://community.cartalk.com/u/John111)\ **Post date:** [January 31, 2019, 8:22am UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/31 "2019-01-31T08:22:27Z")
I use Shell 93 octane or BP 93 octane, bought from the same store’s most of the time. Its a used 2010 Yukon 5.3L. Doesn’t burn any oil. It’s not a daily driver, Most Trip’s are over 60 miles (round-trip) miles, and trips consisting of city driving, with mostly two lane raural roads at 55 mph. ---
**Author:** ![Whitey](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/whitey/32/24680_2.png) [@Whitey](https://community.cartalk.com/u/Whitey)\ **Post date:** [January 31, 2019, 3:28pm UTC](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523/32 "2019-01-31T15:28:20Z")
If you can afford to use name brand high octane fuel in a Yukon, you probably aren’t hurting for money, but in case anyone else is interested, the GMC Yukon’s owner’s manual only recommends 91 octane, and it will run on 87 octane gasoline without damaging the engine, although the performance might be slightly diminished. Anything above 91 octane in your vehicle is clearly a waste of money. Anything above 87 octane _might_ be a waste of money, but it’s debatable depending on fuel pricing. Oh, and one last thing: I seriously doubt the brand or octane of the fuel affects the level of soot in your exhaust system. The brands you choose, being top tier gasolines, might make a difference in other engine components, like the valves and injectors, but the octane and the brand aren’t likely to change the cleanliness of the inside of your muffler. [Previous page](https://community.cartalk.com/t/is-your-tailpipe-black-inside/133523.md?page=1)