Black soot on exhaust tips

[arunka007]

The exhaust tips of my 4 month old 2016 CX-5 is blackened with soot and looks like this. My finger gets black when I wipe it.

Don't have this problem in my 2005 Lancer. This car is 10 years old, 125k miles and the tips look clean (except for some rust) like this. No black soot. My fingers don't get black when I wipe it.

I had a 2008 Accord until 4 months back and didn't have this issue in that car also.

Is this typical for CX-5? If not, what's going on and what can I do fix it? Is this because the engine might be burning oil?

 

[Unobtanium]

It may be due to running pig rich in the mornings on a cold-start. Remember the CX-5 is a DI motor. I don't know how that impacts things, honestly, but it might. Oil consumption should be measured via the dipstick.

 

[craigo]

This is normal and because of the way the exhaust system works. It is not oil. http://www.mazda.com/en/innovation/technology/skyactiv/skyactiv-g/

I'm summarizing extensively here. The fuel efficiency is realized in part because of the high compression the engine achieves. High compression normally means knocking however, so they put in different type of exhaust header that keeps hot exhaust gas away from the cylinders.

When the car is first started, the emissions reducing catalyst is too cold for good operation and because of the long exhaust header, would take awhile to heat up. So for a moment the engine runs a different mode, slightly rough, with some unburned carbons. This results in some soot on the exhaust tips. After a few seconds the catalyst is at operating temperature and normal operation resumes.

You may have noticed how the engine sounds quite different after starting on a cold morning. That's the system in action.

 

[ryan4130]

The exhaust you are comparing it to is just the pipe with no stainless steel beauty cover. All cars I have seen that have a beauty cover around the actual exhaust pipe have this. It is normal. Just clean it when you wash your car. My gf has a mazda3 and after many years I had to take stainless steel polisher to the beauty tip to completely clean away this black exhaust stuff.

 

[Unobtanium]

It honestly sounds like a bit of piston-slap, to me. I think there is some inherent in the engine design due to the short-skirt pistons, etc.

 

[arunka007]

It may be due to running pig rich in the mornings on a cold-start. Remember the CX-5 is a DI motor. I don't know how that impacts things, honestly, but it might. Oil consumption should be measured via the dipstick.

What does "running pig rich" mean? I always wait for the RPM to drop to 1000 before I put the car in Drive gear, if that's what you meant.

 

[arunka007]

The exhaust you are comparing it to is just the pipe with no stainless steel beauty cover. All cars I have seen that have a beauty cover around the actual exhaust pipe have this. It is normal.

This is not true in my experience. My 2008 Accord EX-L had the steel cover. It looked great till it was totaled this year.

 

[arunka007]

This is normal and because of the way the exhaust system works. It is not oil. http://www.mazda.com/en/innovation/technology/skyactiv/skyactiv-g/

I'm summarizing extensively here. The fuel efficiency is realized in part because of the high compression the engine achieves. High compression normally means knocking however, so they put in different type of exhaust header that keeps hot exhaust gas away from the cylinders.

When the car is first started, the emissions reducing catalyst is too cold for good operation and because of the long exhaust header, would take awhile to heat up. So for a moment the engine runs a different mode, slightly rough, with some unburned carbons. This results in some soot on the exhaust tips. After a few seconds the catalyst is at operating temperature and normal operation resumes.

You may have noticed how the engine sounds quite different after starting on a cold morning. That's the system in action.

Does this mean all Skyactiv cars will have this problem, if i can call it that?

 

[banjos-n-beer]

My previous 2014 Mazda 3 had/got the soot, as does my current 2016 CX5. You just have to clean the tips every few weeks or so, unless you don't care how they look.

 

[craigo]

Does this mean all Skyactiv cars will have this problem, if i can call it that?

Correct, it's an inherent part of the design. Some of the early skyactiv engines that didn't have the 4-2-1 header might not have it, but that's limited to some of the previous generation mazda3's. By "Pig rich" he means a rich fuel mixture is used during that mode. This heats things up faster but increases the amount of unburned carbons - the soot you see. The benefit of heating up the catalyst faster offsets this negative.

 

[arunka007]

As an engineer (not Mechanical obviously) I really appreciate all the details in you guys' replies. Thanks!

 

[rockthebeef]

What does "running pig rich" mean?

Running "rich" means that there is more fuel in the air/fuel mixture than what would be considered normal. Cars tend to run rich at cold startup.

Normal is 14.7:1 air:fuel. This is the right ratio for complete chemical combustion.

 

[ALafya]

GDI engines produce more soot in general because their operation mode is somewhat more similar to a Diesel engine.
http://www.aqmd.gov/docs/default-so...onference/session6_5_mattimaricq.pdf?sfvrsn=2

Main reason is the less than homogeneous air/fuel mixture at the cylinder, compared with port injection where the mixture is better and thus very low levels of soot.

 

[mazdadude]

Running "rich" means that there is more fuel in the air/fuel mixture than what would be considered normal. Cars tend to run rich at cold startup.

Normal is 14.7:1 air:fuel. This is the right ratio for complete chemical combustion.

For longevity reasons, you would prefer to have an engine running towards rich instead of lean.

 

[boandlkramer]

My Bimmer has it too. Its pretty common.

I don't see it as a "problem"


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[erhayes]

Normal

 

[Woodys2718]

My 14 Touring looked like that and so does my 16 GT.

 

[MidwestCX5]

What about the white residue?

 

[Hank3]

All four of our Mazdas ('02 Protege Sedan, '03 Protege5, '10 Mazda5, '08 Mazdaspeed3) have been like this. As another member mentioned, Mazdas run rich and this is normal. Either clean regularly or let it be

I use Eagle One Never Dull to keep them clean:

 

[Sekmor]

So what does it mean when the pipe is perfectly clean? From day 1, our '14 always had the black soot around the pipe, a normal thing to wash every week. But the last few months I notice it is no longer there.
I would rather not have the soot, but it's sort of weird that it quit appearing, obviously it's running different, good or bad (uhm)