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Why is Carb Heat less of an issue on Lycoming Engines? and if this is true, how much less of an issue is it?

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It's because the spider duct that connects the carb to the intake runners going to the cylinders is cast into the oil sump and the carb mounts directly to that. So the carb gets a lot of engine heat that warms the carb body by conduction. Also, it's getting radiant heat from the sump directly above.

On Continentals the carb is insulated from the engine by its mounting and location relative to the sump. Continentals without pressure cowls like J-3 Cubs are the worst for carb ice formation.

Carb icing is relatively rare on Lycomings but is still possible if the conditions are sufficiently favourable, so you still have to use normal carb heat protocols.

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  • $\begingroup$ I get regular icing in Lycoming o-320 equipped c172s while at low cruise and taxi power, but I am in a cool humid climate. not every flight but frequent $\endgroup$ – Max Power Mar 10 '19 at 22:19
  • $\begingroup$ Yeah at say 65F and 90% humidity you will get it on Lycs. My glider club's Pawnee with an Lyc O-540 appears to have had a carb ice incident lately. My own O-290 has never shown signs of carb ice. Knock on wood. $\endgroup$ – John K Mar 10 '19 at 22:39
  • $\begingroup$ I had a pair of Lyc O-320s (150hp) ice up during cruise in an Apache. I've never had an icing problem in TCMs. Just one more datapoint... $\endgroup$ – acpilot Mar 10 '19 at 22:40
  • $\begingroup$ Not a big event in any case, engine gets a little rough or low on power, add heat for a minute then remove heat and increase throttle a bit to reduce recurrence. If I even suspect due to weather I will carb heat for 10-20 seconds to see if it makes a change. $\endgroup$ – Max Power Mar 10 '19 at 23:19
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I think the question is incorrect - should be why is carb icing less of an issue on Pipers vs Cessnas when they are carburated. And then it comes to carb placement. On Pipers, the carb is in a warmer place vs Cessnas and thus less susceptible to icing.

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