Soot in tail pipe = Oil burning ?

[Dominik]

Hello,
This may be a simple question but it really puzzles me. I Istuck my finger in the tail pipe of my 2003 4 cyl Altima ( 88,000 km) and I found a really thick black soot, did the same with my '95 Saab 2.3L 4 cyl (211,000 km) and there was a lot less soot my finger was barely black.
Now both cars do not burn much oil Altima needs about 0.25 l top-up between 6,000 km oil changes the Saab the same, none of the cars smoke wheter during morning starup or under heavy acceleration. Could this mean heavy carbon deposits in the combustion chamber and on the valves? I was considering Bardhal's "No Smoke" combustion chamber cleaner, it claims to clean carbon of the valves and combustion chambers, is this stuff any good??
I am affraid that it may affect the cat (it' just been replaced during recal service)
Would synthetic oil help here? the Altima gets Dealer service oil and when I change it Pennzoil Conventional 10w30 or Havoline Synthetic 5W-40 from my old stock.

 

[Thatwouldbegreat]

Black soot is usually the engine running a little rich.

Might be normal for athat car, or maybe abn oxygen sensor?

If the car runs normally, I'd run some injector cleaner and give the car some full throttle driving on entrance ramps and drive it for an hour or more.

I used to set up carbs to run a dark grey...a whitish grey was an indication that it was lean.

 

[Vesta]

This will occur when using conventional oil. I changed my car over to synthetic when it had just a few thousand kms on it. At the same time i cleaned the inside of the exhaust pipe (removing all the black soot). It now has over 80,000kms on it and i can still see the sanding marks on the pipe, no soot! Just another reason why i like synthetics so much.

 

[Triple_Se7en]

When/if the above suggestions don't work, change to another brand of spark plugs.

 

[vad]

Check out other similar Altimas.
If they're equally dirty then it's "normal" for this engine design.
In that case I don't think that switching to a synthetic would make any difference.

 

[W.T.McGlynn]

Could be normal.
Was last smog check showing it was running rich ?
Try some "Redline" Injector cleaner.
Switch to "Chevron" gasoline.
Good Luck.......

 

[V1]

I disagree with the conventional oil theory here. I used synthetic in my civic with soot in exhaust. My Mazda6 gets conventional; no soot at all for 40k miles. It's mostly fuel or emission control related.

 

[mechtech]

You catalytic converter may be puked.
It's rare to see real soot in the pipe, nowadays.
If it's from oil, it will feel a little greasy. Soot from fuel is rather dry.

 

[vad]

What's the real soot?

Regarding the black tail pipes.
The most cars have from somewhat dirty to very dirty ones.
Your clean finger stuck in one of those will show some or a lot "black stuff" on it.
I actually have condacted some unscientific survey of the Ford Focus cars.
The ones produced with the old Zetec engine had exceptionally clean, I would say pristine looking tail pipes, regardless of mileage.
When Ford has switched the Focus to a new Mazda designed engine, the tailpipes don't look as pristine anymore. (in both the Focus and Mazda3 sharing basically the same motors).
Emisson controls, combustion process tuning parameters and even the exaust pipe design might be at play.

 

[bulwnkl]

Reading the original post, I see that the catalyst was just replaced under recall. If it wasn't working properly, that's probably why there's soot in the tailpipe. Soot is from a slightly rich mixture, or in your case probably from the catalyst not properly catalyzing everything in the exhaust.

 

[vad]

I don't think that a bad cat would have any effect on soot since the Cats just reduce CO and HC but don't trap particles.

 

[JohnBrowning]

All vechiles are different. THe type of fuel and the quality of fuel has a huge impact on this. You also have issues like how much wattervapor is being pushed through the exhaust. A vechile that pass's more water vapor theough the exhaust will have a cleaner looking exhaust. THe type of driveing one does also has an impact on this. It has little to do with oil burning in most cases! My 2003 Camry has only burnt enough oil to be detected on the dipstick 1 time since I have owned it. It does though have a black tailpipe!

 

[sanitarium16]

Ever since i got my off road h pipe put on my pipes are covered in soot!

 

[Ramblin Fever]

Same engine type doesn't always mean anything.

My pipe is clear and clean, and very rusty looking after 140k miles. Look at several other vehicles with the same engine, there pipes are black.

Dino versus synthetic - I don't believe that matters, as I've ran dino for the first 139K miles.

 

[brianl703]

It might also have to do with the number of cold startups since not only is the cat not effective until it heats up to operating temperature, but the mixture is driven rich by the computer due to low coolant temperature.

 

[Ugly3]

I have looked at many car tailpipes just driving down the street. Maybe 80% are sooty black. My guess is that it is not necessarily a problem. My tailpipe was black until I added FP60 to my fuel. Now the tailpipe is clean.

 

[Quest]

light fluffy soot, just a thin coating--cat is functional and engine is properly tuned (proper A/F ratio from cold startup to normal operating temp --*closed loop for EFI vehicles*)

heavy soot, dry-- excessive fuel during cold starts or lazy/non functional cat.Sometimes, an overly rich or *lame-mode" EFI engine while closed loop maybe the cause.

Occasionally, this could be the first sign of valve guide wear (morning sickness--blue puff of smoke during morning startup or deceleration).

wet soot, oily smell--- general oil burning. This, depending of the situation, could be burnt turbo bearing, stuck oil control ring packs or excessive valve guide clearance.

 

[Ray H]

The type of driving will strongly influence the amount of soot depeosits in the exhaust system. Constant highway speeds in which the engine operates closest to stoichometric fuel-air mixtures will show the least soot buildup. Stop-'n-go city driving - especially in cold environments, just the opposite. Catalytic converters are not designed to "trap" soot, but they will efficiently convert it to carbon dioxide unless they're overwhelmed by fuel-rich circumstances such as the above urban and/or low temperature driving circumstances or frequent engine shutdowns and restarts. A bad O2 sensor could also affect soot amount. Synthetic vs. conventional oil per se in a healthy engine? Do the letters, "B" and "S", have any meaning in your lexicon, dear reader? (Perhaps in a situation of poor ring sealing and sheared back or improperly chosen low viscosity oil, excess blowby would conceivably lead to increased soot deposits, though . . .)

 

[Amkeer]

I agree with Brian and Ray. The soot deposits you see are normal byproducts of combustion in a cold start-up or stop and go driving cycle. Until the vehicle reaches operating temperature it will burn rich.