Smoky Exhaust Occasionally, Only on Full Throttle ???
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Joined: Nov 2009
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'20 GLS450, '17 S550 Sedan
Smoky Exhaust Occasionally, Only on Full Throttle ???
I occasionally see SMOKE in my rear-view mirror, when I'm driving and quickly apply full throttle (2017 S550 4-Matic w/ the M278 engine, 79k miles, No Check Engine Light).
Parameters: Engine warmed up 190-200F. Already in motion, on the freeway going 55mph and then flooring it to get up to 80mph. Or when turning onto the freeway on-ramp at 35mph and flooring it to get up to 70mph, to merge.
It never happens twice in quick succession. For example, if I've just floored it and seen the smoke in the rear-view mirror... and then I slow back down and repeat the same process, there's zero smoke the second time.
Maybe there's something to "burn off" and once it's burned off, then it's gone for a while, until it builds up again?
I'm still under Mercedes Extended Warranty for another week, and I have an appointment in a couple days.
What should I ask for, at the dealership? Is there a test? Will the ELW even cover them doing anything, since the CEL is not illuminated?
THANK YOU in advance for your wisdom!
Parameters: Engine warmed up 190-200F. Already in motion, on the freeway going 55mph and then flooring it to get up to 80mph. Or when turning onto the freeway on-ramp at 35mph and flooring it to get up to 70mph, to merge.
It never happens twice in quick succession. For example, if I've just floored it and seen the smoke in the rear-view mirror... and then I slow back down and repeat the same process, there's zero smoke the second time.
Maybe there's something to "burn off" and once it's burned off, then it's gone for a while, until it builds up again?
I'm still under Mercedes Extended Warranty for another week, and I have an appointment in a couple days.
What should I ask for, at the dealership? Is there a test? Will the ELW even cover them doing anything, since the CEL is not illuminated?
THANK YOU in advance for your wisdom!
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From: Fort Worth TX
2020 S560, 2014 SLK55 (Prev. 2016 S65, 2013 SLK350, 2008 CLS63, 2006 E350, 2006 CLS500, 2005 C230K)
If you can see it in the rearview you probably have a problem. Blue or black smoke?
Part throttle PCV issue would be fist suspect.
Part throttle PCV issue would be fist suspect.
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Had: 1987 300TD, Had: 2004 C230 Sport Sedan, Have: 2014 E350 Sport, Have: 2019 S450
If it appears only 1 time when you go WOT, then it’s likely residual soot/moisture in the exhaust system, being blown out the tailpipe due to the high flow rate under WOT.
If it appears with every WOT application, then it may warrant further investigation.
If it appears with every WOT application, then it may warrant further investigation.
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From: Phoenix
222 S-65
Black smoke is full throttle enrichment. You and those behind you will see it but it shouldn’t block out visibility of cars behind.
Blue smoke is oil.
White smoke is water in exhaust due to condensation or coolant or a failing injector dumping fuel (which won’t be intermittent).
Blue smoke is oil.
White smoke is water in exhaust due to condensation or coolant or a failing injector dumping fuel (which won’t be intermittent).
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W212 FL
If it were a major problem it could have been all the time but that doesn't mean there won't be anything in the future related to the smokes you described . If you don't smell anything , it must be something fairly good . If I were you , I could ask dealer's to take a test drive . Nothing can replace a real time even to me
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From: Phoenix
222 S-65
Can be! My 221 S-65 when under load for a long time 30 or more minutes up a big mountain pass or serious honing in 80+ degree ambient temperatures would deliver blue smoke that would block the view behind me. Get out of the power a few minutes for cooling (coolant temperature never over 190 and oil temp never over 230) and smoke is gone until another extended period of time under load. Did that the whole time I owned it. Obviously oil. Never cared enough to chase after it as it ran perfectly. Learned to expect it. I figure likely crankcase vapors over powering itself.
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S600
My guess is that you are Blowing the Carbon out of it.
Pre-catalyst cars would do this--we called it blowing the carbon out--also known as "Italian Tune up" when used at a stop.
It happens sporadically because the carbon has to build up before the high temperatures and pressures of full throttle can break it off the cylinder, heads, manifold, and maybe even the cats.
If the smoke (particles actually) thins down and then stops after a second or three while still accelerating at full throttle:: that indicates blowing the carbon out, too.
Pre-catalyst cars would do this--we called it blowing the carbon out--also known as "Italian Tune up" when used at a stop.
It happens sporadically because the carbon has to build up before the high temperatures and pressures of full throttle can break it off the cylinder, heads, manifold, and maybe even the cats.
If the smoke (particles actually) thins down and then stops after a second or three while still accelerating at full throttle:: that indicates blowing the carbon out, too.
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Thread Starter
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Joined: Nov 2009
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'20 GLS450, '17 S550 Sedan
Yes, I had the car at the dealership yesterday, and I spoke to two technicians (foreman and tech) about the occasional smoke. They both concluded that it was most likely carbon buildup. Thank you all for your replies!
"Italian Tune-up" -- I love it!
"Italian Tune-up" -- I love it!
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2018 S560
These cars with the direct injection you gotta run hard once in a while to keep the engines clean. I do a bottle of chevron injection cleaner once every 10K miles or so too.
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My guess is that you are Blowing the Carbon out of it.
Pre-catalyst cars would do this--we called it blowing the carbon out--also known as "Italian Tune up" when used at a stop.
It happens sporadically because the carbon has to build up before the high temperatures and pressures of full throttle can break it off the cylinder, heads, manifold, and maybe even the cats.
If the smoke (particles actually) thins down and then stops after a second or three while still accelerating at full throttle:: that indicates blowing the carbon out, too.
Pre-catalyst cars would do this--we called it blowing the carbon out--also known as "Italian Tune up" when used at a stop.
It happens sporadically because the carbon has to build up before the high temperatures and pressures of full throttle can break it off the cylinder, heads, manifold, and maybe even the cats.
If the smoke (particles actually) thins down and then stops after a second or three while still accelerating at full throttle:: that indicates blowing the carbon out, too.
Although cars are not humans, you could think of them in a way that gymnastics or general exercise helps them, they need to stretch their legs every once in a while.
Last edited by W205C43PFL; Feb 7, 2025 at 03:26 PM.
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From: Cincinnati
2010 E350 4Matic
I have often wondered whether full throttle accelerations were a net benefit to the life of the car or not. I never do if unless called upon by a driving situation. My guidance comes from Click and Clack that encouraged people to drive their cars gently if they wanted to maximize their longivity.
The only thing I know for certain is that the stresses on the drivetrain parts are increased with a full throttle acceleration.
The only thing I know for certain is that the stresses on the drivetrain parts are increased with a full throttle acceleration.
Last edited by MBNUT1; Feb 8, 2025 at 10:08 AM.
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S600
I have often wondered whether full throttle accelerations were a net benefit to the life of the car or not. I never do if unless called upon by a driving situation. My guidance comes from Click and Clack that encouraged people to drive their cars gently if they wanted to maximize their longivity.
a) car has water temp at 190ºF
b) car has oil tempt at 190ºF
c) tires are up to temperature with adequate tread
d) road surface is clean and dry
With the above, one can floor the throttle and run the ending up to read line with essentially no wear on the engine, and perhaps blowing out carbon buildup will actually be good for the car and its engine (compared to allowing the carbon to continue to build up.
(a) if the water temp is not up to temp, you may be doing heat-related-stress damage to the engine.
(b) engines used on track suffer greater wear more because the oil gets hot 270ºF-300ºF, thins viscosity and allows metal to metal contact. At 212ºF (100ºC) xW-40 oil has a viscosity of 12.5-15.0 centiStokes, that same oil (pre shear) at 275ºF will have a viscosity of ~7 cST and at 300ºF ~3.5 cSt. At 13 cSt, the oil film can hold 4× as much force than an oil at ~3.5 cST; another way to look at it is:: IF an oil film at 13 cSt can hold moving parts 4 microns apart, the oil film at 3.5 cST can only hold them 1 micron apart. Should the oil have particles big enough to bridge the gap, the bearing and journals will wear. Is is really as simple as that. Oil without particles in it will not cause wear until metal to metal contact creates those particles (or blow by introduces the particles).
If your full throttle time is under 1% of engine on use with above caveats, it won't do anything other than consume gasoline.
