How do you use Carburetor Temperature Gauge

[Kevin Holbrook]

I am flying a Cessna 172N with O-360-A4M, carbureted, of course. I use the carb heat pretty much as taught during flying lessons and per the POH / checklists...

As part of an avionics upgrade, I now have carb temperature displayed on the EMS, along with alerts. For now, it's information that is just there, but I don't use it.

For those who fly carbureted engines with a carb temp gauge, does it change how you use carb heat? Do you find yourself using it less, or more, or no differently?

 

[PaulS]

Good question, I've never used one. I suspect that if the gage starts getting near freezing, you apply carb heat. Hopefully someone will chime in.

 

[Stewartb]

I’ve had a carb heat gauge in my Cessna 180 since I got it 27 years ago. My carb temp is in the caution zone 90% of the time. I disregarded it when I had a round instrument and never selected it once I changed to a digital instrument. Some guys think their goal in flying is to keep carb temp above freezing. I haven’t found that to be useful in any way in my own plane.

 

[Clip4]

They are generally rather worthless.

 

[Tantalum]

Similar, a few of our club planes have it, and one of the newer archers have it as well.. in the Archer it does not show you a temperature, just an annunciator

It's basically always telling you (me) either 'caution' or that there's ice

So in my experience, fly it per the poh and how you were taught. The gauge is a data point but a not very useful one

Actually, almost to the contrary I've heard of people inducing carb ice by using just a little bit of carb heat to appease the gauge only to have carb ice form deeper down the venturi

 

[asicer]

I’ve had a carb heat gauge in my Cessna 180 since I got it 27 years ago. My carb temp is in the caution zone 90% of the time. I disregarded it when I had a round instrument and never selected it once I changed to a digital instrument. Some guys think their goal in flying is to keep carb temp above freezing. I haven’t found that to be useful in any way in my own plane.

And on the opposite end of the spectrum, there's a Lycoming with a side-draft carb that I fly that never gets in the caution zone.

 

[Brad Z]

O-470 Continentals are notorious for ice, so I bought the carb temperature probe for my EDM-830. I agree with other comments, it's basically useless. It's always the temperature for ice unless you add carb heat; no duh. Ice is more a factor of the humidity of the air, which the carb temp probe provides zero information about. Like others, I fly as specified in the POH and periodically apply carb ice when I'm in conditions that are conducive to carb icing.

FWIW- my old flying club had a 182 and we added an Iceman carb ice detector. Apparently the detector has a led light beam and photo resistor to detect the accumulation of ice. The thing was a pain and would altert for ice right at start up. I believe the lens would frequently cloud over with particulates, causing the alarm to think there was ice. We eventually just turned it off.

 

[Dan Thomas]

Ice is more a factor of the humidity of the air, which the carb temp probe provides zero information about.

Yup. Training and knowledge are better than electronic or mechanical doodads. One needs to check the METARs before flying. Look at the temperature and dewpoint, and consult whatever chart your POH might have. If not, the web has lots of them.

 

[Sinistar]

Probably the best thing for it is a INOP sticker that fully covers it.

Actually what would have been a better solution would have been a simple user adjustable MP alarm. Climb up to cruise, lean out and set prop. Then set a manifold pressure alarm for just a bit under the cruise value.

When flying the 182 around any kind of visible moisture you just look at MP more often.

 

[Albany Tom]

Not answering the original question, but I believe the best way to spot carb ice in cruise in a fixed pitch plane is to watch RPM. Get to your altitude, trim and lean, and leave the settings be. If RPM drops and the engine runs a little rough, try that carb heat thing. Works great!

Have picked up carb ice in cruise twice in PA-28's, 150 and 180. They're really not known for ice what what I've heard, but it happens. Once in daytime, warm humid day, maybe 500-800' below a fully overcast layer. The second time at night, clear skies but yep, warm and humid, over the Hudson River valley. No big deal in either case, but at night it woke me up a bit.

I'll do precautionary carb heat in descent all the time, in narrow temp/dewpoints nearly always on final, and 100% with cubs starting in downwind, but I've never done precautionary carb heat in cruise. Seems counter-productive. But in a plane that likes to make ice, like cubs, you pay attention to the power you're getting, always.

 

[Wagondriver]

I use it to know when I do NOT need carb heat, like when I pull the power to land. Carb temp us often over 85 with the throttle closed.
I have an o-520, it has iced up in downwind, and has iced up on take off. I watch the carb temp on take off, if it’s a little humid, or a lot humid, I’ll pull some heat, enough to see it well above freezing, if the engine chokes on a load of water I keep it on, if not it’s off.

my engine runs very nicely lean if peak, at certain power settings and temperatures. If it’s super cold out, fuel distribution is crap, but I know what carb temps equal a smoother running engine.

 

[Stewartb]

Hmm. My Alaskan 0-520 is very different from yours. Carb heat unnecessary. Every pilot needs to know his own airplane. My 180 CHT/EGT spreads are every bit as good as my balanced injected Cub engine.