Cruise Carb Temperature

Discussion in 'Flight Following' started by CT583, Nov 15, 2021.

  1. CT583

    CT583 Pre-Flight

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    For those of you who have a carb temperature gauge of some sort....
    What temperature do you prefer to keep your carburetor at during cruise flight?

    I have a JPI with a carb temp sensor. I couldn’t find any solid answers on the topic, so I’ve been keeping my carb temp around 37-38 deg F during cruise flight.
    Well for all flight situations really.
    I just adjust the mixture to lean out the richness of the carb heat application.

    I’m wondering if this is the norm or if I’m being overly cautious.
    Living on the Texas coast, we almost always have humidity, so my mindset is better safe than sorry.
    I know the O-470 is an ice machine and thankfully I’ve never encountered it.

    Thanks
     
  2. GeorgeC

    GeorgeC Administrator Management Council Member PoA Supporter

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    I might cycle the heat occasionally in cruise, but otherwise, there is no target temperature.
     
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  3. Huckster79

    Huckster79 Pattern Altitude

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    thats exactly what I do… especially being I fly a known ice maker (and I know you do too). Seems to work just fine giving her a hit now n again, though I always do it for a good 15-30 seconds when I do.
     
  4. Clip4

    Clip4 Final Approach

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    There is no operational need to hear the carb in cruise flight.
     
  5. Zeldman

    Zeldman Touchdown! Greaser!

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    I'm gonna guess a anything above 32F....

    (I know, there is one in every crowd...)
     
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  6. Jeff Oslick

    Jeff Oslick En-Route PoA Supporter

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    O-470-50 (PPonk) in a C182:

    I typically add heat to low 40s F. This isn't for carb ice, but because the induction system in an O-470 is absolute garbage. Adding some carb heat evens-out the temperature spread on the EGTs between the right and left cylinders, allowing for more uniform leaning between the cylinders.
     
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  7. WDD

    WDD En-Route

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    I've never found a reason to turn the carb heat on when cruising. Besides, when cruising at altitude, the air is already getting thinner - heating it up and loosing density / putting even less mass of O2 into the cylinders isn't going to help. I fly Skyhawks and Skylanes BTW.
     
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  8. midwestpa24

    midwestpa24 En-Route

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    I've only ever encountered carb ice once while in cruise. Let's just say given the conditions at the time, it was less than surprising, and was almost the least of my worries.

    I've never run carb heat in cruise in VFR conditions, ever, and we fly when it is darn cold up here in the north country. Granted when it's that cold, there usually isn't much moisture either. Keep that in mind, cold temps alone don't create ice. Moisture is needed as well, either as visible moisture or high humidity.
     
    Last edited: Nov 15, 2021
  9. CT583

    CT583 Pre-Flight

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    I noticed more uniform EGT as well after adding some carb heat.

    the results appear to be split between: dont need it, to keeping carb above freezing temps.
     
  10. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    I encountered cruise ice once at a few hundred AGL with nothing but trees as far as you could see except for the railroad tracks I was following. It was a worry.

    Not usually a problem because you have yea olde throttle pushed in and the pressure drop across the carburetor is small resulting in only a small drop in temperature. (Yes, you get some drop in temperature due to fuel evaporating - but most of the evaporation happens downstream of the carburetor.)

    But, OAT above freezing, Carb below freezing, add some humidity, whatcha gonna get?
     
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  11. Jeff Oslick

    Jeff Oslick En-Route PoA Supporter

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    This is a technique I learned from taking the Skylane Systems & Proceedures course that Cessna Pilots Association offers (I took it many years ago when John Frank taught it).
     
  12. Randomskylane

    Randomskylane Pre-Flight

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    Is there a target temp? Thanks
     
  13. Jeff Oslick

    Jeff Oslick En-Route PoA Supporter

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    No, you would pick the coldest carb temp that works to smooth out the EGTs to allow more uniform leaning. If it is cold dry air, that could be at or below freezing (I've had that happen a couple times at or about 10,000'). Of course you need EGTs (and you should have CHTs) on each cylinder.
     
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