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#1
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Exhaust pipe on one side is sooty
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. |
#2
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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. |
#3
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"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 |
#4
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"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. |
#5
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Casey Wilson wrote:
"Peter Duniho" wrote in message ... "Casey Wilson" N2310D @ gmail.com wrote in message news:jsire.3592$1q5.2647@trnddc02... This last weekend, I was helping wash down a Cessna-150. The port side of the belly was pretty sooty as was the exhaust pipe. The starboard exhaust seems fine. Is that normal? Or is there some impending failure implied? Soot might be an indication of burning oil, or it could simply be the result of an overly-rich mixture. AFAIK, the color of the soot provides some information: grey or whitish soot is likely to be burned oil, while darker black soot is likely to be incompletely burned fuel. But how about this particular case when only one side is sooty, Pete. I'm not Pete. Could the spiraling airflow direct the exhaust toward the cowling on one side, and away from the cowling on the other? ... or are we talking about the soot actually inside the pipe? Dave |
#6
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I'm not Pete. Could the spiraling airflow direct the exhaust toward the cowling on one side, and away from the cowling on the other? ... or are we talking about the soot actually inside the pipe? Dave I'm talking about soot in the pipe. Right side is dusty brownish -- left side is black grimy. |
#7
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Casey Wilson wrote:
I'm not Pete. Could the spiraling airflow direct the exhaust toward the cowling on one side, and away from the cowling on the other? ... or are we talking about the soot actually inside the pipe? Dave I'm talking about soot in the pipe. Right side is dusty brownish -- left side is black grimy. Have you had a change in oil consumption of late? If the black soot is fairly dry, then it sounds like a rich mixture in one or both or all three cylinders sharing that pipe (I forget which model this was now). If it is wet/oily, then it sounds like you are burning oil instead of, or in addition to, having a rich mixture. Matt |
#8
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"Casey Wilson" N2310D @ gmail.com wrote in message news:TPlre.2467$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. |
#9
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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. |
#10
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"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 |
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