Exhaust pipe on one side is sooty

[Casey Wilson]

This last weekend, I was helping wash down a Cessna-150. The port side
of the belly was pretty sooty as was the exhaust pipe. The starboard exhaust
seems fine. Is that normal? Or is there some impending failure implied?
The airplane is a rental and the last couple 100-hour checks don't
reveal any problem, nor does the last annual.

[Sport Pilot]

Casey Wilson wrote:
> This last weekend, I was helping wash down a Cessna-150. The port side
> of the belly was pretty sooty as was the exhaust pipe. The starboard exhaust
> seems fine. Is that normal? Or is there some impending failure implied?
> The airplane is a rental and the last couple 100-hour checks don't
> reveal any problem, nor does the last annual.

Many years ago I owned a C150 with an auto gas STC. The exhaust would
get sooty on car gas. Seems like the right side was worse (not a navy
plane so right is right), but that could just be coincidence.

[Peter Duniho]

"Casey Wilson" <N2310D @ gmail.com> wrote in message
news:jsire.3592$1q5.2647@trnddc02...
> This last weekend, I was helping wash down a Cessna-150. The port side
> of the belly was pretty sooty as was the exhaust pipe. The starboard
> exhaust seems fine. Is that normal? Or is there some impending failure
> implied?

Soot might be an indication of burning oil, or it could simply be the result
of an overly-rich mixture. AFAIK, the color of the soot provides some
information: grey or whitish soot is likely to be burned oil, while darker
black soot is likely to be incompletely burned fuel.

I would say that in either case, it's not necessarily "normal", except
inasmuch as a rental airplane used primarily for training may be operated at
full rich almost 100% of the time, much of that time when the mixture should
have been leaned. So black soot may not be a cause for concern in that
instance, especially if the engine otherwise seems to be running fine and
fuel consumption isn't excessive.

IMHO, the best way to determine what's "normal" is to look at the other
airplanes on the ramp. If similar airplanes used for similar purposes have
similar appearance, it's normal. Otherwise, it's not. :)

Pete

[Casey Wilson]

"Peter Duniho" > wrote in message
...
> "Casey Wilson" <N2310D @ gmail.com> wrote in message
> news:jsire.3592$1q5.2647@trnddc02...
>> This last weekend, I was helping wash down a Cessna-150. The port
>> side of the belly was pretty sooty as was the exhaust pipe. The starboard
>> exhaust seems fine. Is that normal? Or is there some impending failure
>> implied?
>
> Soot might be an indication of burning oil, or it could simply be the
> result of an overly-rich mixture. AFAIK, the color of the soot provides
> some information: grey or whitish soot is likely to be burned oil, while
> darker black soot is likely to be incompletely burned fuel.

But how about this particular case when only one side is sooty, Pete.

[Dave Butler]

Casey Wilson wrote:
> "Peter Duniho" > wrote in message
> ...
>
>>"Casey Wilson" <N2310D @ gmail.com> wrote in message
>>news:jsire.3592$1q5.2647@trnddc02...
>>
>>> This last weekend, I was helping wash down a Cessna-150. The port
>>>side of the belly was pretty sooty as was the exhaust pipe. The starboard
>>>exhaust seems fine. Is that normal? Or is there some impending failure
>>>implied?
>>
>>Soot might be an indication of burning oil, or it could simply be the
>>result of an overly-rich mixture. AFAIK, the color of the soot provides
>>some information: grey or whitish soot is likely to be burned oil, while
>>darker black soot is likely to be incompletely burned fuel.
>
>
> But how about this particular case when only one side is sooty, Pete.

I'm not Pete. Could the spiraling airflow direct the exhaust toward the cowling
on one side, and away from the cowling on the other? ... or are we talking about
the soot actually inside the pipe?

Dave

[George Patterson]

Casey Wilson wrote:
> This last weekend, I was helping wash down a Cessna-150. The port side
> of the belly was pretty sooty as was the exhaust pipe. The starboard exhaust
> seems fine. Is that normal? Or is there some impending failure implied?

Might be burning oil. Rub your finger down the inside of the pipe when it's
cold. If you come out with a gooey black mess, it's pumping oil. Come out with
black sooty residue, it's burning oil. Running rich will also cause a sooty
residue, but it will be more of a grey.

Now. Do the same thing with the other pipe. If the two pipes are about the same
and it's an oil problem, it's probably caused by normal wear on the engine (how
many hours SMOH?). If one pipe is much worse than the other, you probably have a
problem with a single cylinder. If the two pipes are about the same and
indications point to running rich, the CFIs aren't teaching their students to
lean. This will also be the case if the vast majority of operations are done
near full throttle or below 3,000' (IOW, typical student operations).

George Patterson
Why do men's hearts beat faster, knees get weak, throats become dry,
and they think irrationally when a woman wears leather clothing?
Because she smells like a new truck.

[Casey Wilson]

>
> I'm not Pete. Could the spiraling airflow direct the exhaust toward the
> cowling on one side, and away from the cowling on the other? ... or are we
> talking about the soot actually inside the pipe?
>
> Dave

I'm talking about soot in the pipe. Right side is dusty brownish -- left
side is black grimy.

[Matt Whiting]

Casey Wilson wrote:

>>I'm not Pete. Could the spiraling airflow direct the exhaust toward the
>>cowling on one side, and away from the cowling on the other? ... or are we
>>talking about the soot actually inside the pipe?
>>
>>Dave
>
>
> I'm talking about soot in the pipe. Right side is dusty brownish -- left
> side is black grimy.
>
>

Have you had a change in oil consumption of late? If the black soot is
fairly dry, then it sounds like a rich mixture in one or both or all
three cylinders sharing that pipe (I forget which model this was now).
If it is wet/oily, then it sounds like you are burning oil instead of,
or in addition to, having a rich mixture.


Matt

[Dave Stadt]

"Casey Wilson" <N2310D @ gmail.com> wrote in message
news:TPlre.2467$kj5.211@trnddc03...
> >
> > I'm not Pete. Could the spiraling airflow direct the exhaust toward the
> > cowling on one side, and away from the cowling on the other? ... or are
we
> > talking about the soot actually inside the pipe?
> >
> > Dave
>
> I'm talking about soot in the pipe. Right side is dusty brownish --
left
> side is black grimy.
>


Fuel distribution in carbureted engines is notoriously uneven. Could be one
cylinder on the sooty side is running quite a but richer that the other
three.

[Peter Duniho]

"Casey Wilson" <N2310D @ gmail.com> wrote in message
news:15kre.3603$1q5.2104@trnddc02...
> But how about this particular case when only one side is sooty, Pete.

I'm not clear on your question. Do you mean "one side of the aircraft"?
Whether there's a harmful problem or simply a benign aspect of the
particular operation going on, it wouldn't be surprising for only one side
of the engine exhaust to be affected. As a (completely irrelevant :) )
example, consider the success of GAMI and their "matched injectors". In
most cases, each cylinder is operating under a very specific, and often
quite unique relative to the other cylinders, set of conditions. This is
true even during normal operation of the engine.

In terms of this specific issue, an overly rich mixture may only be causing
enough unburned fuel to result in noticeable soot on one side (even when the
mixture is technically too rich for all cylinders). Or, you could have a
serious problem such as some portion of the priming system leaking into the
engine during regular operation. The former is probably nothing to worry
about; the latter would be cause for grounding the airplane. :)

Of course, as far as the primer theory goes, it could be as simple as
someone failing to secure the primer knob before starting the engine. I
admit, I don't have personal knowledge of the details of the priming system
on the 150, so I don't know if it primes only one side of the engine. But
I'm pretty sure that configuration exists on other airplanes, so it might on
the 150.

In any case, all of the above assumes black soot, indicating a rich mixture.
If you're burning oil (white/grey soot) to that degree, then there's
probably something serious going on whether or not the effect is symmetric.
You haven't described the soot in greater detail, so we're still doing the
"if it's this, then...if it's that, then" dance. :)

As far as the maintenance checks go...I assume that the 100-hour and annual
inspections all included a compression check, which *might* provide
information about the condition of the piston rings. But regardless, the
failure to uncover a cause for a problem is not proof that there's no
problem. It certainly seems to me that, as long as the source of the soot
is undetermined, and as long as there is not a similar effect on other
airplanes on the ramp, someone ought to be trying to figure out what's
causing the soot. It may turn out to be completely benign, but you'd want
to know that for sure, rather than just guessing.

Pete

[nrp]

Maybe a minor air leak in the intake system on the leaner side? The
intake gaskets have a straight side & I've seen them suck in. Maybe a
loose hose clamp?

A leaking primer is also a possibility - as I recall they usually only
prime on one side.

A test would be to apprach under power, land and check immediately,
avoiding any taxi at low power & see if it is fouling at cruise. I'd
be concerned if the black stuff is generated on one side at cruise.

[[email protected]]

This calls for a compression check and a timing check on the engine.

[Mike Rapoport]

> wrote in message
oups.com...
> This calls for a compression check and a timing check on the engine.
>

What would a timing check accomplish?

Mike
MU-2

[Peter Duniho]

"nrp" > wrote in message
oups.com...
> Maybe a minor air leak in the intake system on the leaner side?

That's a good point. Just because the symptom is on one side, that doesn't
mean that the problem isn't on the other.

[RST Engineering]

Absolutely nothing. The man is a jerknose.

Jim



> What would a timing check accomplish?
>
> Mike
> MU-2
>
>

[George Patterson]

Casey Wilson wrote:
>
> I'm talking about soot in the pipe. Right side is dusty brownish -- left
> side is black grimy.

Either burning or pumping oil. Check the plugs on those cylinders -- if the
ceramic is also black and sooty, that's the cylinder with the problem.
Compression tests are in order. If the black grime is deamp and smeary, suspect
a broken ring.

George Patterson
Why do men's hearts beat faster, knees get weak, throats become dry,
and they think irrationally when a woman wears leather clothing?
Because she smells like a new truck.