C182P: Carb Temp in Cruise

AggieMike88

AggieMike88

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The original "I don't know it all" of aviation.
Yesterday afternoon / evening, I performed a flight out to Brady Texas (KBBD) and back delivery a Pilots-n-Paws Christmas cat to a very greatful new owner.

55WB, a 1975 C182P, is equipped with a carb temp gauge. Once I had established my cruise altitude (4500 msl), I took a look at this gauge and saw 18°F displayed. Engine was performing well, but I decided to pull the carb heat about half way. Reading on the gauge went up to about 38°F, and I heard for the first time carb ice being ingested by the engine.

I flew the rest of the flight with the carb heat pulled into that position, except for landing when I had it fully deployed.

This is my first winter to do this much flying, especially cross country flights of 1.0-1.5 hrs of cruising. What is the proper procedure for using carb heat? During landing and low power for sure, but what about other phases of the flight?
 
Back when I was getting my PPL we had a Cessna 182 we flew for the Civil Air Patrol. Those continental engines have the carb far away from the engine IIRC and thus are very prone to carb ice. We didn't have a carb temp gauge but did have a carb ice indicator. It would come on about every 15 minutes during a cold cruise. We just got in the habit of pulling the carb heat every so often, enjoying the satisfying sound of carb ice being ingested, and continuing on our merry way. I saw nothing wrong with this method but if the carb ice was in danger of stalling the engine then I would run with half carb heat. If you rent wet then fuel doesn't really matter, run with half heat all the time.
 
Also, does carb heat skip the intake filter? I remember some reason why it wasn't the best idea to run it all the time besides economy.
 
JasonM said:
I recieved some good feedback on this thread. Should be helpful for you: http://www.pilotsofamerica.com/forum/showthread.php?t=64354

From my gained knowledge on carb ice, I will not use partial carb heat anymore.
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Great thread, thanks for the link. It would appear that carb heat and cold weather operations could use a little more emphasis during training. If I recall all my training was "do this when the checklist says so."
 
tehmightypirate said:
Great thread, thanks for the link. It would appear that carb heat and cold weather operations could use a little more emphasis during training. If I recall all my training was "do this when the checklist says so."
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I agree.

My training was in a 2004 DA20, so fuel injection and no discussion of carb ice beyond the textbook info.
 
Due to their susceptibility to carb ice, many (if not most) carbureted C-182's have carb air temp gauges. If you have one, then it's a good idea any time the needle gets into the yellow zone to pull just enough carb heat to get the needle back up out of that zone. The exception to this is on the ground or in dusty air, for the reason stated above (bypasses the air filter). However, most of the time, once above pattern altitude, the air is dust-free enough that cruising with partial carb heat isn't deleterious to engine health (places like LA's smog layer excepted).
 
As an owner of same engine / aircraft without a temp gauge, I respectfully disagree.

The gauge gives you a hint that there's a possibility for carb ice. No need to pull the handle if there's no other indications of carb ice actually happening.

You're just letting a thermometer become the pilot.
 
denverpilot said:
As an owner of same engine / aircraft without a temp gauge, I respectfully disagree.

The gauge gives you a hint that there's a possibility for carb ice. No need to pull the handle if there's no other indications of carb ice actually happening.

You're just letting a thermometer become the pilot.
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I disagree with this, especially the last statement. What you're doing is using all the tools you have available to operate the engine in the safest and most efficient manner possible. I'm not saying that a CAT gauge is essential, or that you can't such a plane fly safely without one, but if you have something that tells you of an impending problem, and allows you to adjust the controls to prevent it, there's no reason not to use it.
 
I agree, our old 182 had a carb temp gauge and the new one doesn't. I normally fly at fairly high power settings, 70%+, I occasionally pull the carb heat in cruise to see if I am getting carb ice, but I don't recall ever flying with the carb heat on partially. I do use it on low power decents, especially with higher humidity. :D
denverpilot said:
As an owner of same engine / aircraft without a temp gauge, I respectfully disagree.

The gauge gives you a hint that there's a possibility for carb ice. No need to pull the handle if there's no other indications of carb ice actually happening.

You're just letting a thermometer become the pilot.
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tehmightypirate said:
Also, does carb heat skip the intake filter? I remember some reason why it wasn't the best idea to run it all the time besides economy.
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It bypasses the filter to act as an alternate air source. Filters can get clogged by snow or ice crystals. Injected engines don't have carb heat but they still have alternate air doors.

I'm often surprised that pilots sometimes don't know that carb heat is an alternate air source. Similarly, the magneto switch is there not just to test the mags in the runup and to shut them off after the flight, but to shut off a roque magneto that starts firing when it shouldn't and making the engine lose a pile of power.

Dan
 
Ron Levy said:
I disagree with this, especially the last statement. What you're doing is using all the tools you have available to operate the engine in the safest and most efficient manner possible. I'm not saying that a CAT gauge is essential, or that you can't such a plane fly safely without one, but if you have something that tells you of an impending problem, and allows you to adjust the controls to prevent it, there's no reason not to use it.
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The whole damn flight is an "impending problem". Better land and find a different hobby.

Pulling the handle will fix the problem nearly instantly if it ever occurs.

Cirrus pilots on the other hand... They'd better pull their little red handle before they even take off. ;)
 
Ron Levy said:
I disagree with this, especially the last statement. What you're doing is using all the tools you have available to operate the engine in the safest and most efficient manner possible. I'm not saying that a CAT gauge is essential, or that you can't such a plane fly safely without one, but if you have something that tells you of an impending problem, and allows you to adjust the controls to prevent it, there's no reason not to use it.
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The MP pressure gage is a tool. Like Nate said, the carb temp gage is only a thermometer.
 
denverpilot said:
The whole damn flight is an "impending problem". Better land and find a different hobby.

Pulling the handle will fix the problem nearly instantly if it ever occurs.

Cirrus pilots on the other hand... They'd better pull their little red handle before they even take off. ;)
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As a CFI, I can't tell people not to ignore the CAT gauge and wait for carb ice to actually form before pulling the carb heat the way you seem to do. And your analogy is completely inappropriate.
 
timwinters said:
The MP pressure gage is a tool. Like Nate said, the carb temp gage is only a thermometer.
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...just like the oil temp gauge. Would you suggest not doing anything about an oil temperature passing the redline and waiting until the engine showed actual signs of failure before doing something?
 
Ron Levy said:
...just like the oil temp gauge. Would you suggest not doing anything about an oil temperature passing the redline and waiting until the engine showed actual signs of failure before doing something?
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Apples...oranges.

Oil temp redline is an issue.

Carb temp yellow arc MAY BE an issue if other parameters are also aligned. The MP gage will tell you if you're developing ice but the carb temp gage tells you nothing on its own.
 
In TX I'll use carb heat sparingly when I think there may be ice forming and use it for long enough to clear it then back off. I remember climbing out of the top of the red dust at 7000'.
 
timwinters said:
Whatever Ron.
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I'd say you're both right. From a Cessna 182Q POH under inadvertent icing:

Watch for signs of carburetor air filter ice and apply carburetor heat as required. An unexplained loss in manifold pressure could be caused by carburetor ice or air intake filter ice. Lean the mixture if carburetor heat is used continuously.
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Then from the section on carburetor icing:

An unexplained drop in manifold pressure and eventual engine roughness may result from the formation of carburetor ice. To clear the ice, apply full throttle and pull the carburetor heat knob full out until the engine runs smoothly; then remove carburetor heat and readjust the throttle. If conditions require the continued use of carburetor heat in cruise flight, use the minimum amount of heat necessary to prevent ice from forming and lean the mixture for smoothest engine operation.
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So, for what it's worth, Cessna recommends if you get carb ice then use the carb heat (duh, right?). If you get continuous carb ice then use the minimum continuous heat required and lean the mixture for the warmer air.
 
I'm not going to turn in the power I get from the cold air, to fight my way through the tick air unless I actually need to. If I wanted to keep the thing out of the yellow arc about the only time the carb heat would be off would be for landing!
 
Ron Levy said:
As a CFI, I can't tell people not to ignore the CAT gauge and wait for carb ice to actually form before pulling the carb heat the way you seem to do. And your analogy is completely inappropriate.
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Sure you can. "That gauge indicates the temperature is right inside the carb for icing. It doesn't mean icing is occurring. Note your manifold pressure and if it falls, take appropriate action -- knowing it might be carb ice. It could also be far more serious. The action you'll take is the exact same action you would have taken without the gauge, since it's right here on the checklist. But you don't need the checklist at first because you already know the power loss drill, right? And now you may or may not have a hint as to what's happening."

The "analogy" was a joke. I forgot. You have no humor genes. ;)
 
I have a continental 0-470 with a carb temp guage. I don't pull it unless MP or sound or some other nuance confirms carb ice.

I've heard the guys who say your flooding your engine if you don't lean with it on, but I don't subscribe to that. It robs power, and it does open the airway to straight un-filtered atmosphere.

However, just out of habit, and according to the POH, I do pull it when it's been in the yellow after a long cruise during my let down. Maybe I don't need to, but like owning a gun, I'd rather have it and not need it, than need it and not have it. :wink2:
 
By the way, that second one in the POH surprises more pilots than carb ice. Especially in snow / ice.

Plugging up the air filter will act very similarly to carb ice, and that cute little thermometer gauge won't show it happening.
 
tehmightypirate said:
I'd say you're both right. From a Cessna 182Q POH under inadvertent icing:
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Hmmm...I didn't see any mention of the carb temp gage in either of those POH sections. It appear to me like they both clearly stated to watch the MP gage for assistance in determining if you're developing ice. :rolleyes:

Skylane81E said:
I'm not going to turn in the power I get from the cold air, to fight my way through the thick air unless I actually need to. If I wanted to keep the thing out of the yellow arc about the only time the carb heat would be off would be for landing!
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Agree completely, Dunc. I used to drink the "warm the air to 50dF" tea but no longer do. This heating wasn't for carb ice though. The warm air supposedly kept the fuel better atomized in the fuel/air mixture and thus more evenly distributed the fuel mixture to all cylinders and the engine ran smother.

Mine didn't. And this was confirmed by the difference in EGT spreads being negligible.

It robbed me of a lot of power though.
 
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So can someone describe the sound of an engine ingesting carb ice?
 
tehmightypirate said:
So, for what it's worth, Cessna recommends if you get carb ice then use the carb heat (duh, right?). If you get continuous carb ice then use the minimum continuous heat required and lean the mixture for the warmer air.
Click to expand...

Leaning the mixture was something I didn't do more of when I had carb heat going on. I did the normal lean procedure before I had noted the carb temp. But didn't think about "re-applying" once the additional heat was added. Thanks for the reminder.
 
BillTIZ said:
It tends to "stumble", run a little rough and then clear.
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When I first applied the heat, this is what I heard. A quick reduction in the "normal" noise for that power setting, then a clearer "more powerful" sound with no changes to throttle or prop. That told me that the constriction had cleared and the engine was getting the correct amount of airflow.
 
AggieMike88 said:
Leaning the mixture was something I didn't do more of when I had carb heat going on. I did the normal lean procedure before I had noted the carb temp. But didn't think about "re-applying" once the additional heat was added. Thanks for the reminder.
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Does yours have an EGT guage? If you lean, then later pull the carb heat, you will see the EGT will go cooler and you can lean some more.

Keep an eye on your CHT. You can fry your jugs.
 
Henning said:
Rrrrrrrrrrrrrrr brrap rrrbrap rapp brrrrrrrrrrrrrrrr.....:D
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So, kinda like burrito night?

My ice ingestion felt and sounded like the engine skipped a beat. A bit of a backwards jolt and a brief gap in sound, then normal behavior. But, this was an application of full power, not carb heat. I picked up carb ice waiting at the hold short line and melted it on takeoff. The engine stumbled at 400 AGL.
 
AggieMike88 said:
When I first applied the heat, this is what I heard. A quick reduction in the "normal" noise for that power setting, then a clearer "more powerful" sound with no changes to throttle or prop. That told me that the constriction had cleared and the engine was getting the correct amount of airflow.
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Carb heat richness the mixture so if you are leaving it on you should readjust for that.
 
Carb heat won't get rid of ice in the air filter, it will only bypass the clogged filter. Completely different problem with a completely different cause and totally unrelated to carb air temperature. The gauge which tells you that carb air filter icing may happen is your OAT gauge, in conjunction with your eyes telling you you're in visible moisture.
 
Ron Levy said:
Carb heat won't get rid of ice in the air filter, it will only bypass the clogged filter. Completely different problem with a completely different cause and totally unrelated to carb air temperature. The gauge which tells you that carb air filter icing may happen is your OAT gauge, in conjunction with your eyes telling you you're in visible moisture.
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Not to mention that you have to be in some thick IMC to get the filter to ice or snow jam.
 
Ron Levy said:
...just like the oil temp gauge. Would you suggest not doing anything about an oil temperature passing the redline and waiting until the engine showed actual signs of failure before doing something?
Click to expand...

You need a certain combination of temperature and humidity for carb ice to develop. The temp gauge only tells you one of these variables. Many times you can be in the right temperature zone for carb ice and you can fly there all day and not pick up a trace.

Considering the engine makes more power with colder, more dense air I don't use carb heat unless it's necessary.

If the gauge is in the yellow, be alert for carb ice. As someone suggested earlier it is a good idea to pull carb heat occasionally to check and see if you are picking up any carb ice. I do this habitually even if I don't have a carb temp gauge.


Sent from my iPhone using Tapatalk
 
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I've never understood how to use CAT. I have the JPI carb temp probe going into an EDM-700 and it always show ambient minus a few degrees when the engine is running. Of course applying carb heat raises the temperature quickly. The probe is on the piston side of the throttle plate and I would have thought the air would have been a lot colder in the vacuum environment, maybe 50 degrees colder than ambient, which would tell a more useful story.

So if a CAT reads ~ ambient temperature only, as mine does, what is it telling me that my OAT gauge isn't?
 
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